Patent Publication Number: US-2021186028-A1

Title: Compositions and methods for treating liberibacter diseases and other bacterial diseases

Description:
BACKGROUND 
     Huanglongbing (HLB), also called  citrus  greening, is one of the most devastating  citrus  plant diseases. This  citrus  plant disease causes multibillion-dollar loss annually in the United States alone. According to research from the Institute of Food and Agricultural Sciences at the University of Florida, Florida has lost approximately 162,200 acres of  citrus  plants and 7,513 jobs since detection of HLB in Florida in 2005. The most recent forecasts from the National Association of Academies of Science predicted that  citrus  production from 2016 to 2017 is approximately 70% lower than peak production levels from 1997 to 1998. Moreover, HLB also spreads rapidly in Texas and California. Recently, more than 400 confirmed cases of HLB-infected trees have been reported in southern California. HLB is caused by the phloem-limited Gram-negative bacteria of the  Liberibacter  species, e.g.,  Candidatus Liberibacter  species (e.g.,  Candidatus Liberibacter asiaticus  (Ca. L.  asiaticus )), which is transmitted by insects of the Psyllidae family, e.g., Asian  citrus  psyllids (ACP). 
     Another important disease cause by the  Liberibacter  species is Potato Zebra Chip (ZC) disease, also called Potato Zebra complex disease. ZC disease is associated with  Candidatus Liberibacter solanacearum  ( Ca. L. solanacearum ), which is transmitted by potato psyllids (e.g.,  Bactericera cockerelli ). ZC disease reached epidemic level in northern Texas in 2006 and has spread to Arizona, California, Colorado, Idaho, Oregon, Kansas, Nebraska, and New Mexico. ZC disease has caused millions of dollars loss to the potato industry in the southwestern United States, particularly Texas. In addition to potato, other solanaceous crops, including tomato, eggplant and pepper, can also be infected. There exists a need in the art for innovative compositions and methods to treat diseases in plants caused by  Liberibacter  species (e.g.,  Candidatus Liberibacter  species). 
     SUMMARY 
     The disclosure provides stable antimicrobial (e.g., antibacterial or antifungal or both) peptides (SAMPs) that may be used in methods of preventing or treating bacterial diseases, such as those caused by Gram-negative bacteria, e.g., a  Liberibacter  disease (e.g.,  citrus  greening disease (also called Huanglongbing (HLB)) or potato Zebra Chip disease) in plants (e.g.,  citrus  plants or potato plants). The SAMPs disclosed herein may be heat stable, as well as stable in plant extracts and/or in plant lysates (e.g.,  citrus  lysates). The SAMPs described herein can effectively inhibit/kill different bacteria species, such as Gram-negative bacterial species, e.g.,  Liberibacter  species, for example,  Candidatus Liberibacter asiaticus  ( C. Las ) that infects  citrus, Candidatus Liberibacter solanacearum  that infects all solanaceous plants, and  Liberibacter crescens , which is a culturable bacterium that infects  papaya. Liberibacter crescens  can be used as a surrogate for the unculturable  Candidatus Liberibacter  species (e.g.,  C. Las ). Furthermore, the SAMPs disclosed herein can also inhibit and kill other bacterial pathogens (e.g., other Gram-negative bacterial pathogens), such as  Agrobacterium tumefaciens  (also known as  Rhizobium radiobacter ) and  Pseudomonas syringae  strains.  Agrobacterium tumefaciens  can cause crown gall disease or tumors in more than 140 eudicot species. Different strains of  Pseudomonas syringae  can cause bacterial canker or blast diseases on many dicot and monocot crops. 
     In one aspect, the disclosure features an isolated stable antimicrobial (e.g., antibacterial or antifungal or both) peptide (SAMP) comprising a sequence that is substantially identical (e.g., at least 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94% 95%, 96%, 97%, 98%, or 99% identical) to a sequence of any one of SEQ ID NOs:1-13 and 35-37. In some embodiments, the peptide comprises a sequence having at least 75% sequence identity (e.g., at least 80%, 85%, 90%, 91%, 92%, 93%, 94% 95%, 96%, 97%, 98%, or 99% sequence identity) to a sequence of any one of SEQ ID NOs:1-13 and 35-37. In particular embodiments, the peptide comprises a sequence having at least 75% sequence identity (e.g., at least 80%, 85%, 90%, 91%, 92%, 93%, 94% 95%, 96%, 97%, 98%, or 99% sequence identity) to a sequence of any one of SEQ ID NOs:1 and 2. 
     In another aspect, the disclosure features an isolated stable antimicrobial (e.g., antibacterial) peptide (SAMP) comprising a sequence of 
     X 1 GX 2 X 3 VSX 4 ENX 5 X 6 QGFX 7 HX 8 FEX 9 TFX 10 SX 11 EGX 12 AEYX 13 X 14 HPX 15 HVEX 16 ANX 17  X 18 LX 19 X 20 LEKX 21 LX 22 X 23 DYKPX 24 TX 25 RV (SEQ ID NO:27), in which X 1  is R, K, or W; X 2  is K or E; X 3  is N or D; X 4  is T or I; X 5  is L, F, or R; X 6  is H or Q; X 7  is P or T; X 8  is I, L, or V; X 9  is S or F; X 10  is E or D; X 11  is T or L; X 12  is V or I; X 13  is V or I; X 14  is S, A, or D; X 15  is S, A, or V; X 16  is Y or F; X 17  is L or T; X 18  is F, M, or L; X 19  is A, P, or T; X 20  is N or Q; X 21  is V or F; X 22  is V or I; X 23  is V or I; X 24  is T, E, or Q; and X 25  is V, E, L. 
     In some embodiments of this aspect, the isolated SAMP comprising a sequence of SEQ ID NO:27, in which X 1  in SEQ ID NO:27 is R; X 2  is K; X 3  is N; X 4  is I; X 5  is L; X 6  is H; X 10  is E; X 11  is T; X 12  is V; X 13  is V; X 16  is Y; X 17  is L; X 18  is F; X 19  is A; X 20  is N; X 21  is V; X 22  is V, X 23  is I; and X 24  is T. 
     In another aspect, the disclosure features an agricultural composition comprising an isolated stable antimicrobial (e.g., antibacterial) peptide (SAMP) described herein. The agricultural composition may further comprise at least one of an herbicide, an herbicide safener, a surfactant, a fungicide, a pesticide, a nematicide, a plant activator, a synergist, a plant growth regulator, an insect repellant, an acaricide, a molluscicide, or a fertilizer. 
     In another aspect, the disclosure features a nucleic acid molecule encoding an isolated stable antimicrobial (e.g., antibacterial) peptide (SAMP) described herein. Also provided is a polynucleotide comprising a promoter operably linked to the nucleic acid molecule (optionally where the promoter is heterologous to the nucleic acid molecule). The disclosure also features a cell comprising the nucleic acid molecule of the previous aspect. In some embodiments, the cell is a bacterial, yeast, plant, insect, or mammalian (e.g., human) cell. In particular embodiments, the cell is a plant cell. 
     In another aspect, the disclosure features a plant comprising an isolated stable antimicrobial (e.g., antibacterial) peptide (SAMP) described herein or the polynucleotide discussed above or the nucleic acid molecule encoding an isolated SAMP described herein. In some embodiments, the plant is a  citrus  plant or a solanaceous plant. In some embodiments, the plant is more tolerant to a bacterial pathogen compared to a control plant (otherwise identical) in which the SAMP is absent. 
     In another aspect, the disclosure features a plant comprising an in situ altered stable antimicrobial (e.g., antibacterial) peptide (SAMP) comprising at least one amino acid substitution corresponding to an amino acid at any one of positions X 1  to X 25  as set forth in SEQ ID NO:27, wherein the mutated SAMP provides  Liberibacter  disease (e.g., Huanglongbing (HLB)) resistance or  Liberibacter  disease (e.g., HLB) tolerance,  Pseudomonas  disease (e.g., bacterial canker or blast diseases) resistance or  Pseudomonas  disease tolerance, or  Agrobacterium  disease (e g., Crown Gall disease or tumors) resistance or  Agrobacterium  disease tolerance to the plant. 
     In another aspect, the disclosure features an expression cassette comprising a promoter operably linked to a polynucleotide encoding an isolated stable antimicrobial (e.g., antibacterial) peptide (SAMP) described herein, wherein introduction of the expression cassette into a plant results in the plant having enhanced  Liberibacter  disease (e.g., HLB) resistance or  Liberibacter  disease (e.g., HLB) tolerance,  Pseudomonas  disease (e.g., bacterial canker or blast diseases) resistance or  Pseudomonas  disease tolerance, or  Agrobacterium  disease (e g., Crown Gall disease or tumors) resistance or  Agrobacterium  disease tolerance. In some embodiments, the promoter of the expression cassette is heterologous to the polynucleotide. In some embodiments, the promoter is inducible. In some embodiments, the promoter is plant tissue-specific (e.g., phloem-specific, tuber-specific, root-specific, stem-specific, trunk-specific, or leaf-specific. In some embodiments, the phloem-specific promoter is the sucrose transporter protein SUC2 promoter. 
     In another aspect, the disclosure features a transgenic plant comprising the expression cassette of the previous aspect, wherein the plant has enhanced  Liberibacter  disease (e.g., HLB) resistance or  Liberibacter  disease (e.g., HLB) tolerance,  Pseudomonas  disease (e.g., bacterial canker or blast diseases) resistance or  Pseudomonas  disease tolerance, or  Agrobacterium  disease (e g., Crown Gall disease or tumors) resistance or  Agrobacterium  disease tolerance, as compared to a control plant lacking the expression cassette. In some embodiments, the transgenic plant is a  citrus  plant or a solanaceous plant. 
     In another aspect, the disclosure features a method of preventing or treating a  Liberibacter  disease (e.g., HLB), a  Pseudomonas  disease (e.g., bacterial canker or blast diseases), or an  Agrobacterium  disease (e.g., Crown Gall disease or tumors) in a plant by contacting the plant with an isolated stable antimicrobial (e.g., antibacterial) peptide (SAMP) described herein or an agricultural composition comprising an isolated SAMP. In some embodiments of these aspects, the isolated peptide or agricultural composition is injected into the trunk of the plant. In some embodiments, the isolated peptide or agricultural composition is injected into the stem of the plant. In other embodiments, the isolated peptide or agricultural composition is foliar sprayed onto the plant. In other embodiments, the isolated peptide or agricultural composition is applied to the root of the plant. In other embodiments, the isolated peptide or agricultural composition is applied to the plant by dripping irrigation to the roots. In other embodiments, the isolated peptide or agricultural composition is applied by laser ablation. 
     In another aspect, the disclosure features a method of preventing or treating potato Zebra Chip (ZC) disease in a plant by contacting the plant with an isolated stable antimicrobial (e.g., antibacterial) peptide (SAMP) described herein or an agricultural composition comprising an isolated SAMP. In yet another aspect, the disclosure features a method of preventing or treating a bacterial infection in a plant caused by bacteria in the genus  Liberibacter  (e.g.,  Candidatus Liberibacter  species or  Liberibacter crescens ) by contacting the plant with an isolated SAMP described herein or an agricultural composition comprising an isolated SAMP. In still another aspect, the disclosure features a method of preventing or treating a bacterial infection in a plant caused by bacteria in the genus  Agrobacterium  (e.g.,  Agrobacterium tumefaciens  species) by contacting the plant with an isolated SAMP described herein or an agricultural composition comprising an isolated SAMP. In still yet another aspect, the disclosure features a method of preventing or treating a bacterial infection in a plant caused by bacteria in the genus  Pseudomonas  (e.g.,  Pseudomonas syringae  species) by contacting the plant with an isolated SAMP described herein or an agricultural composition comprising an isolated SAMP. 
     In another aspect, the disclosure features a method of inhibiting the growth of bacteria or killing bacteria in the genus  Liberibacter  (e.g.,  Candidatus Liberibacter  species or  Liberibacter crescens ) in a plant by contacting the plant with an isolated stable antimicrobial (e.g., antibacterial) peptide (SAMP) described herein or an agricultural composition comprising an isolated SAMP. In yet another aspect, the disclosure features a method of inhibiting the growth of bacteria or killing bacteria in the genus  Agrobacterium  (e.g.,  Agrobacterium tumefaciens  species) in a plant by contacting the plant with an isolated stable antimicrobial (e.g., antibacterial) peptide (SAMP) described herein or an agricultural composition comprising an isolated SAMP. In still yet another aspect, the disclosure features a method of inhibiting the growth of bacteria or killing bacteria in the genus  Pseudomonas  (e.g.,  Pseudomonas syringae  species) in a plant by contacting the plant with an isolated stable antimicrobial (e.g., antibacterial) peptide (SAMP) described herein or an agricultural composition comprising an isolated SAMP. 
     In another aspect, the disclosure features a method of preventing or treating a  Liberibacter  disease (e.g., HLB) in a plant or preventing or treating a bacterial infection in a plant caused by bacteria in the genus  Liberibacter  (e.g.,  Candidatus Liberibacter  species (e.g.,  Candidatus Liberibacter asiaticus, Candidatus Liberibacter africanus , and  Candidatus Liberibacter americanus ) or  Liberibacter crescens ) by introducing an expression cassette described herein (e.g., an expression cassette comprising a promoter operably linked to a polynucleotide encoding an isolated stable antimicrobial (e.g., antibacterial) peptide described herein) into the plant. In another aspect, the disclosure features a method of preventing or treating potato ZC disease in a plant or preventing or treating a bacterial infection in a plant caused by bacteria in the genus  Liberibacter  (e.g.,  Candidatus Liberibacter  species (e.g.,  Candidatus Liberibacter solanacearum  (Ca. L.  solanacearum )) or  Liberibacter crescens ) by introducing an expression cassette described herein (e.g., an expression cassette comprising a promoter operably linked to a polynucleotide encoding an isolated SAMP described herein) into the plant. 
     In yet another aspect, the disclosure features a method of preventing or treating a  Pseudomonas  disease (e.g., bacterial canker or blast diseases) in a plant or preventing or treating a bacterial infection in a plant caused by bacteria in the genus  Pseudomonas  (e.g.,  Pseudomonas syringae  species) by introducing an expression cassette described herein (e.g., an expression cassette comprising a promoter operably linked to a polynucleotide encoding an isolated stable antimicrobial (e.g., antibacterial) peptide described herein) into the plant. 
     In still yet another aspect, the disclosure features a method of preventing or treating a  Agrobacterium  disease (e.g., Crown Gall disease or tumors) in a plant or preventing or treating a bacterial infection in a plant caused by bacteria in the genus  Agrobacterium  (e.g.,  Agrobacterium tumefaciens  species) by introducing an expression cassette described herein (e.g., an expression cassette comprising a promoter operably linked to a polynucleotide encoding an isolated stable antimicrobial (e.g., antibacterial) peptide described herein) into the plant. 
     In another aspect, the disclosure features a method of inhibiting the growth of bacteria or killing bacteria in the genus  Liberibacter  (e.g.,  Candidatus Liberibacter  species or  Liberibacter crescens ) in a plant by introducing an expression cassette described herein (e.g., an expression cassette comprising a promoter operably linked to a polynucleotide encoding an isolated stable antimicrobial (e.g., antibacterial) peptide described herein) into the plant. 
     In another aspect, the disclosure features a method of inhibiting the growth of bacteria or killing bacteria in the genus  Agrobacterium  (e.g.,  Agrobacterium tumefaciens  species) in a plant by introducing an expression cassette described herein (e.g., an expression cassette comprising a promoter operably linked to a polynucleotide encoding an isolated stable antimicrobial (e.g., antibacterial) peptide described herein) into the plant. 
     In yet another aspect, the disclosure features a method of inhibiting the growth of bacteria or killing bacteria in the genus  Pseudomonas  (e.g.,  Pseudomonas syringae  species) in a plant by introducing an expression cassette described herein (e.g., an expression cassette comprising a promoter operably linked to a polynucleotide encoding an isolated stable antimicrobial (e.g., antibacterial) peptide described herein) into the plant. 
     In another aspect, the disclosure features a method of producing a plant having enhanced  Liberibacter  disease (e.g., HLB) resistance or  Liberibacter  disease (e.g., HLB) tolerance by introducing an isolated stable antimicrobial (e.g., antibacterial) peptide described herein or an expression cassette comprising a promoter operably linked to a polynucleotide encoding an isolated stable antimicrobial (e.g., antibacterial) peptide into a plurality of plants; and selecting a plant that comprises the isolated peptide or expresses the polynucleotide from the plurality of plants. 
     In another aspect, the disclosure features a method of producing a plant having enhanced potato ZC disease resistance or potato ZC disease tolerance by introducing an isolated stable antimicrobial (e.g., antibacterial) peptide (SAMP) described herein or an expression cassette comprising a promoter operably linked to a polynucleotide encoding an isolated SAMP into a plurality of plants; and selecting a plant that comprises the isolated peptide or expresses the polynucleotide from the plurality of plants. 
     In another aspect, the disclosure features a method of producing a plant having enhanced  Pseudomonas  disease (e.g., bacterial canker or blast diseases) resistance or  Pseudomonas  disease (e.g., bacterial canker or blast diseases) tolerance by introducing an isolated stable antimicrobial (e.g., antibacterial) peptide described herein or an expression cassette comprising a promoter operably linked to a polynucleotide encoding an isolated stable antimicrobial (e.g., antibacterial) peptide into a plurality of plants; and selecting a plant that comprises the isolated peptide or expresses the polynucleotide from the plurality of plants. 
     In another aspect, the disclosure features a method of producing a plant having enhanced  Agrobacterium  disease (e.g., Crown Gall disease or tumors) resistance or  Agrobacterium  disease (e.g., Crown Gall disease or tumors) tolerance by introducing an isolated stable antimicrobial (e.g., antibacterial) peptide described herein or an expression cassette comprising a promoter operably linked to a polynucleotide encoding an isolated stable antimicrobial (e.g., antibacterial) peptide into a plurality of plants; and selecting a plant that comprises the isolated peptide or expresses the polynucleotide from the plurality of plants. 
     In another aspect, the disclosure features a method of producing a plant having enhanced  Liberibacter  disease (e.g., HLB) resistance or  Liberibacter  disease (e.g., HLB) tolerance (i.e., enhanced resistance or tolerance to a bacterial infection caused by bacteria in the genus  Liberibacter  (e.g.,  Candidatus Liberibacter  species (e.g.,  Candidatus Liberibacter  asiaticus, Candidatus  Liberibacter africanus , and  Candidatus Liberibacter americanus ) or  Liberibacter crescens )) by introducing a mutation into a polynucleotide in the plant, wherein the mutated polynucleotide encodes an isolated stable antimicrobial (e.g., antibacterial) peptide described herein (e.g., an isolated SAMP having at least 75% sequence identity to the sequence of SEQ ID NO:1 or 2). In another aspect, the disclosure features a method of producing a plant having enhanced potato ZC disease resistance or potato ZC disease tolerance (i.e., enhanced resistance or tolerance to a bacterial infection caused by bacteria in the genus  Liberibacter  (e.g.,  Candidatus Liberibacter  species (e.g.,  Candidatus Liberibacter solanacearum  ( Ca. L. solanacearum )) or  Liberibacter crescens ) by introducing a mutation into a polynucleotide in the plant, wherein the mutated polynucleotide encodes an isolated stable antimicrobial (e.g., antibacterial) peptide (SAMP) described herein (e.g., an isolated SAMP having at least 75% sequence identity to the sequence of SEQ ID NO:1 or 2). In some embodiments of these aspects, the introducing occurs in situ in the genome of a plant cell. In particular embodiments, the introducing comprises clustered regularly interspaced short palindromic repeats (CRISPR)/Cas genome editing. In some embodiments of these aspects, the plant is a  citrus  plant or a solanaceous plant (e.g., a potato plant). 
     In still another aspect, the disclosure features a method of producing a plant having enhanced  Agrobacterium  disease resistance or  Agrobacterium  disease tolerance (i.e., enhanced resistance or tolerance to a bacterial infection caused by bacteria in the genus  Agrobacterium  (e.g., Crown Gall disease or tumors caused by  Agrobacterium  strains)) by introducing a mutation into a polynucleotide in the plant, wherein the mutated polynucleotide encodes an isolated stable antimicrobial (e.g., antibacterial) peptide (SAMP) described herein (e.g., an isolated SAMP having at least 75% sequence identity to the sequence of SEQ ID NO:1 or 2). In some embodiments of these aspects, the introducing occurs in situ in the genome of a plant cell. In particular embodiments, the introducing comprises clustered regularly interspaced short palindromic repeats (CRISPR)/Cas genome editing. In some embodiments of these aspects, the plant is eudicot plant. 
     In still another aspect, the disclosure features a method of producing a plant having enhanced  Pseudomonas  disease resistance or  Pseudomonas  disease tolerance (i.e., enhanced resistance or tolerance to a bacterial infection caused by bacteria in the genus  Pseudomonas  (e.g., bacterial canker or blast diseases caused by  Pseudomonas  strains)) by introducing a mutation into a polynucleotide in the plant, wherein the mutated polynucleotide encodes an isolated stable antimicrobial (e.g., antibacterial) peptide (SAMP) described herein (e.g., an isolated SAMP having at least 75% sequence identity to the sequence of SEQ ID NO:1 or 2). In some embodiments of these aspects, the introducing occurs in situ in the genome of a plant cell. In particular embodiments, the introducing comprises clustered regularly interspaced short palindromic repeats (CRISPR)/Cas genome editing. In some embodiments of these aspects, the plant is a monocot or dicot plant (e.g., a tomato plant). 
     In any of the compositions or methods described in the present disclosure, the plant may species be from the genus  Citrus  (e.g.,  Citrus maxima, Citrus medica, Citrus micrantha, Citrus reticulate, Citrus aurantiifolia, Citrus aurantium, Citrus latifolia, Citrus limon, Citrus limonia, Citrus paradise, Citrus sinensis , and  Citrus tangerine ) or species from the family Solanaceae (e.g.,  Solanum  spp.,  Capsicum  spp., and  Nicotiana  spp.). Species from the genus  Solanum  include, e.g.,  Solanum tuberosum, Solanum lycopersicum, Solanum melongena, Solanum aviculare, Solanum capsicastrum, Solanum crispum, Solanum laciniatum, Solanum laxum, Solanum pseudocapsicum, Solanum rantonnetii, Solanum seaforthianum , and  Solanum wendlandii . Species from the genus  Capsicum  include, e.g.,  Capsicum annuum, Capsicum baccatum, Capsicum campylopodium, Capsicum cardenasii, Capsicum chacoense, Capsicum cornutum, Capsicum dusenii, Capsicum eximium, Capsicum friburgense, Capsicum frutescens, Capsicum geminifolium, Capsicum havanense, Capsicum lanceolatum, Capsicum lycianthoides, Capsicum minutiflorum, Capsicum mositicum, Capsicum pubescens, Capsicum recurvatum, Capsicum schottianum, Capsicum spina - alba, Capsicum tovarii , and  Capsicum villosum . Species from the genus  Nicotiana  include, e.g.,  Nicotiana acuminate, Nicotiana benthamiana, Nicotiana glauca, Nicotiana longiflora, Nicotiana rustica, Nicotiana tabacum , and  Nicotiana occidentalis.    
     In particular embodiments, the plant is selected from the group consisting of  Citrus  reticulata,  Citrus sinensis, Citrus clementina, Capsicum annuum, Solanum tuberosum, Solanum lycopersicum, Solanum melongena , and  Nitotiana benthamiana . In particular embodiments, the plant is a sweet orange plant ( Citrus sinensis ). In particular embodiments, the plant is a clementine plant ( Citrus  Clementina). In particular embodiments, the plant is a potato plant ( Solanum tuberosum ). In some embodiment, the plant is a vegetable- or fruit-producing plant. 
     In any of the aspects of the disclosure described herein, in some embodiments, the SAMP is a heat stable (HS) peptide. 
     Furthermore, in any of the aspects of the disclosure described herein, in some embodiments, the SAMP may also provide resistance or tolerance to bacterial diseases caused by other bacterial pathogens, such as  Agrobacterium tumefaciens  (also known as  Rhizobium radiobacter ) and  Pseudomonas syringae.    
     Definitions 
     As used herein, the term “ Liberibacter  disease” refers to a disease, such as an infection, caused by bacteria in the genus  Liberibacter  (e.g.,  Candidatus Liberibacter  species or  Liberibacter crescens ). A  Liberibacter  disease may infect plants such as  citrus  plants (e.g., orange, grapefruit, tangerine, lemon, line, key line, papeda, citron, and pomelo) and solanaceous plants (e.g., potato, tomato, eggplant, and pepper). Huanglongbing (HLB) is a type of  Liberibacter  disease that infects  citrus  plants. 
     As used herein, the terms “ citrus  greening disease” and “Huanglongbing (HLB)” refer to a bacterial infection of plants (e.g.,  citrus  plants) caused by bacteria in the genus  Liberibacter  (e.g.,  Candidatus Liberibacter  species (e.g.,  Candidatus Liberibacter asiaticus, Candidatus Liberibacter africanus , and  Candidatus Liberibacter americanus ) or  Liberibacter crescens ). The infection is vectored and transmitted by the Asian  citrus  psyllid,  Diaphorina citri , and the African  citrus  psyllid,  Trioza erytreae . Three different types of HLB are currently known: the heat-tolerant Asian form, and the heat-sensitive African and American forms. 
     As used herein, the term “Potato Zebra Chip (ZC) disease” refers to a bacterial infection of plants (e.g., potato plants) caused by bacteria in the genus  Liberibacter  (e.g.,  Candidatus Liberibacter  species (e.g.,  Candidatus Liberibacter solanacearum  ( Ca. L. solanacearum )) or  Liberibacter crescens ). The infection is vectored and transmitted by potato psyllids (e.g.,  Bactericera cockerelli ). 
     As used herein, the term “ Agrobacterium  disease” refers to a disease, such as an infection, caused by bacteria in the genus  Agrobacterium  (e.g.,  Agrobacterium tumefaciens  species, also known as  Rhizobium radiobacter ).  Agrobacterium  diseases can comprise Crown Gall disease, or tumors, in more than 140 eudicot species. 
     As used herein, the term “ Pseudomonas  disease” refers to a disease, such as an infection, caused by bacteria in the genus  Pseudomonas  (e.g.,  Pseudomonas syringae  species).  Pseudomonas  diseases can comprise bacterial canker or blast diseases on many dicot and monocot crops (e.g., Tomato Bacterial Speck, Tomato Bacterial Spot, and Tomato Bacterial Canker). 
     As used herein, the term “disease resistance” refers to the ability of a plant to not be affected by a  Liberibacter  disease (e.g., HLB),  Agrobacterium  disease, or  Pseudomonas  disease; or infection by  Liberibacter  bacteria (e.g.,  Candidatus Liberibacter  species or  Liberibacter crescens ),  Agrobacterium  bacteria (e.g.,  Agrobacterium tumefaciens  species), or  Pseudomonas  bacteria (e.g.,  Pseudomonas syringae  species). 
     As used herein, the term “disease tolerance” refers to the ability of a plant to continuously grow and survive despite being infected by bacteria (e.g., gram-negative bacteria, such as  Liberibacter  bacteria,  Agrobacterium  bacteria or  Pseudomonas  bacteria). 
     As used herein, the term “ Liberibacter  disease resistance” refers to the ability of a plant to not be affected by a  Liberibacter  disease (e.g., HLB) or infection by  Liberibacter  bacteria (e.g.,  Candidatus Liberibacter  species or  Liberibacter crescens ). 
     As used herein, the term “ Liberibacter  disease tolerance” refers to the ability of a plant to continuously grow and survive despite being infected by  Liberibacter  bacteria (e.g.,  Candidatus Liberibacter  species or  Liberibacter crescens ) or having a  Liberibacter  disease (e.g., HLB). In some embodiments, a plant with a  Liberibacter  disease (e.g., HLB) may show minor symptoms of the disease, such as yellowing of leaves, blotchy mottle of the leaves, zinc-deficiency-like mottle, chlorosis, and reduced fruit yield, but is still able to grow or produce fruit despite the infection. 
     As used herein, the term “potato ZC disease resistance” refers to the ability of a plant to not be affected by potato ZC disease or infection by  Liberibacter  (e.g.,  Candidatus Liberibacter  species (e.g.,  Candidatus Liberibacter solanacearum  (Ca. L.  solanacearum )) or  Liberibacter crescens ) bacteria. 
     As used herein, the term “potato ZC disease tolerance” refers to the ability of a plant to continuously grow and survive despite being infected by  Liberibacter  (e.g.,  Candidatus Liberibacter  species (e.g.,  Candidatus Liberibacter solanacearum  ( Ca. L. solanacearum )) or  Liberibacter crescens ) bacteria or having potato ZC disease. In some embodiments, a plant with potato ZC disease may show minor symptoms of potato ZC disease, such as chlorosis, leaf scorching, swollen nodes, vascular tissue browning, curled leaves, collapsed stolons, enlarged lenticels, vascular tissue browning, medullary ray discoloration, and necrotic flecking of tuber tissue, but is still able to grow or produce potato despite the infection. 
     As used herein, the term “ Agrobacterium  disease resistance” refers to the ability of a plant to not be affected by an  Agrobacterium  disease (e.g., Crown Gall disease) or infection by  Agrobacterium  bacteria (e.g.,  Agrobacterium tumefaciens  species, also known as  Rhizobium radiobacter ). 
     As used herein, the term “ Agrobacterium  disease tolerance” refers to the ability of a plant to continuously grow and survive despite being infected by  Agrobacterium  bacteria (e.g.,  Agrobacterium tumefaciens  species, also known as  Rhizobium radiobacter ) or having an  Agrobacterium  disease (e.g., Crown Gall disease). 
     As used herein, the term “ Pseudomonas  disease resistance” refers to the ability of a plant to not be affected by a  Pseudomonas  disease (e.g., Tomato Bacterial Speck, Tomato Bacterial Spot, and Tomato Bacterial Canker) or infection by  Pseudomonas  bacteria (e.g.,  Agrobacterium tumefaciens  species). 
     As used herein, the term “ Pseudomonas  disease tolerance” refers to the ability of a plant to continuously grow and survive despite being infected by  Pseudomonas  bacteria (e.g.,  Agrobacterium tumefaciens  species) or having a  Pseudomonas  disease (e.g., Tomato Bacterial Speck, Tomato Bacterial Spot, and Tomato Bacterial Canker). 
     As used herein, the term “stable antimicrobial peptides” or “SAMPs” refers to peptides identified in plants that are  Liberibacter  disease-resistant/tolerant (e.g., HLB-resistant/tolerant). Such peptides are expressed at a higher level in  Liberibacter  disease-resistant/tolerant (e.g., HLB-resistant/tolerant) plants than  Liberibacter  disease-susceptible (e.g., HLB-susceptible) plants. These SAMPs may be injected into plants to prevent or treat a  Liberibacter  disease (e.g., HLB). In some embodiments, the isolated SAMPs disclosed herein have antibacterial or antifungal or both properties. In some embodiments, the isolated SAMPs disclosed herein are heat stable (e.g., heat stable (HS) peptides). In some embodiments, the isolated SAMPs disclosed herein are also stable in plant extracts. In further embodiments, the isolated SAMPs disclosed herein are also stable in plant lysates (e.g.,  citrus  lysates). 
     As used herein, the term “agricultural composition” refers to a composition formulated for application to a plant or plant part (e.g., seed, cutting, shoots, etc.). An agricultural composition is typically in liquid form, e.g., for application by spraying or soaking, but can be in a powder for rehydration or application (dusting or dry coating), or gaseous form (e.g., for enclosed environments). The agricultural composition can be concentrated, e.g., for dilution or water or other solvent. An agricultural composition can also include more than one active ingredient, e.g., a SAMP (e.g., an HS peptide) described herein, alone or in combination with a fungicide, herbicide, fertilizer, etc. 
     As used herein, the term “treat” or “treating” a  Liberibacter  disease (e.g., an HLB or a potato ZC disease) in plants refers to the reduction or eradication of symptoms caused by the  Liberibacter  disease by methods described herein. Symptoms of HLB include, but are not limited to, yellowing of leaves, blotchy mottle of the leaves, zinc-deficiency-like mottle, severe chlorosis, and reduced fruit yield. Symptoms of potato ZC disease include, but are not limited to, chlorosis, leaf scorching, swollen nodes, vascular tissue browning, curled leaves, collapsed stolons, enlarged lenticels, vascular tissue browning, medullary ray discoloration, and necrotic flecking of tuber tissue. In some embodiments, the disclosed methods may not necessarily result in eradication or cure of the  Liberibacter  disease (e.g., HLB or potato ZC disease), but can significantly reduce the symptoms caused by the disease. 
     As used herein, the term “prevent” or “preventing” a  Liberibacter  disease (e.g., an HLB or a potato ZC disease) in plants refers protecting a plant that is at risk for the disease from developing the disease, or decreasing the risk that a plant may develop the disease. A plant may be contacted with a SAMP (e.g., an HS peptide) described herein before the plant develops the disease, or shows signs of the disease. 
     As used herein, the term “plant” includes whole plants, shoot vegetative organs/structures (e.g., leaves, stems and tubers), roots, flowers and floral organs/structures (e.g., bracts, sepals, petals, stamens, carpels, anthers and ovules), seed (including embryo, endosperm, and seed coat) and fruit (the mature ovary), plant tissue (e.g., vascular tissue, ground tissue, and the like) and cells (e.g., guard cells, egg cells, and the like), and progeny of same. Plants that can be treated as described herein include, e.g.,  citrus  plants (e.g., orange, grapefruit, tangerine, lemon, line, key line, papeda, citron, and pomelo) and solanaceous plants (e.g., potato, tomato, eggplant, and pepper). 
     The term “plant” also includes naturally occurring mutants and genetically modified plants. A “genetically modified plant” or “transgenic plant” refers to one whose genome has been manipulated so that it is different than a wild-type plant of the same species, variety or cultivar, e.g., to add a gene or genetic element, remove a gene or genetic element, mutate a gene or genetic element, change chromatin structure, change gene or protein expression levels, etc. A transgenic plant may contain an expression vector or cassette. The expression cassette typically comprises a polypeptide-encoding sequence or a modulating nucleic acid (e.g., an antisense, an siRNA or ribozyme) operably linked (i.e., under regulatory control of) to an appropriate inducible or constitutive regulatory sequences that allow for the expression of a polypeptide or modulating nucleic acid. The expression cassette can be introduced into a plant by transformation or by breeding after transformation of a parent plant. Such methods can be used in a whole plant, including seedlings and mature plants, as well as to a plant part, such as seed, fruit, leaf, or root, plant tissue, plant cells or any other plant material, e.g., a plant explant, as well as to progeny thereof, and to in vitro systems that mimic biochemical or cellular components or processes in a cell. In the context of the present disclosure, genetically modified plants may include genetic modifications in a gene encoding a SAMP (e.g., an HS peptide). In some embodiments, the modified gene in the genetically modified plant may encode a SAMP (e.g., an HS peptide) described herein (e.g., a SAMP having at least 75% sequence identity or at least one amino acid substitution relative to the sequence of any one of SEQ ID NOs:1-13 and 35-37 (e.g., SEQ ID NOs:1 and 2)). 
     An “expression cassette” refers to a nucleic acid construct that, when introduced into a host cell, results in transcription and/or translation of an RNA or polypeptide, respectively. 
     As used herein, the term “polynucleotide” refers to an oligonucleotide, or nucleotide, and fragments or portions thereof, and to DNA or RNA of genomic or synthetic origin, which may be single- or double-stranded, and represent the sense or anti-sense strand. A single polynucleotide is translated into a single polypeptide. 
     As used herein, the terms “peptide” and “polypeptide” are used interchangeably and describe a single polymer in which the monomers are amino acid residues which are joined together through amide bonds. A polypeptide is intended to encompass any amino acid sequence, either naturally occurring, recombinant, or synthetically produced. 
     As used herein, the term “substantial identity” or “substantially identical,” used in the context of nucleic acids or polypeptides, refers to a sequence that has at least 50% sequence identity with a reference sequence. Alternatively, percent identity can be any integer from 50% to 100%. In some embodiments, a sequence is substantially identical to a reference sequence if the sequence has at least 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% sequence identity to the reference sequence as determined using the methods described herein; preferably BLAST using standard parameters, as described below. Embodiments of the present disclosure provide for SAMPs (e.g., HS peptides) that are substantially identical to any of SEQ ID NOs:1-13 and 35-37 (SEQ ID NOs:1 and 2). 
     For sequence comparison, typically one sequence acts as a reference sequence, to which test sequences are compared. When using a sequence comparison algorithm, test and reference sequences are entered into a computer, subsequence coordinates are designated, if necessary, and sequence algorithm program parameters are designated. Default program parameters can be used, or alternative parameters can be designated. The sequence comparison algorithm then calculates the percent sequence identities for the test sequences relative to the reference sequence, based on the program parameters. 
     A comparison window includes reference to a segment of any one of a number of contiguous positions, e.g., a segment of at least 10 residues. In some embodiments, the comparison window has from 10 to 600 residues, e.g., about 10 to about 30 residues, about 10 to about 20 residues, about 50 to about 200 residues, or about 100 to about 150 residues, in which a sequence may be compared to a reference sequence of the same number of contiguous positions after the two sequences are optimally aligned. 
     Algorithms that are suitable for determining percent sequence identity and sequence similarity are the BLAST and BLAST 2.0 algorithms, which are described in Altschul et al. (1990)  J. Mol. Biol.  215: 403-410 and Altschul et al. (1977)  Nucleic Acids Res.  25: 3389-3402, respectively. Software for performing BLAST analyses is publicly available through the National Center for Biotechnology Information (NCBI) web site. The algorithm involves first identifying high scoring sequence pairs (HSPs) by identifying short words of length W in the query sequence, which either match or satisfy some positive-valued threshold score T when aligned with a word of the same length in a database sequence. T is referred to as the neighborhood word score threshold (Altschul et at supra). These initial neighborhood word hits act as seeds for initiating searches to find longer HSPs containing them. The word hits are then extended in both directions along each sequence for as far as the cumulative alignment score can be increased. Cumulative scores are calculated using, for nucleotide sequences, the parameters M (reward score for a pair of matching residues; always &gt;0) and N (penalty score for mismatching residues; always &lt;0). For amino acid sequences, a scoring matrix is used to calculate the cumulative score. Extension of the word hits in each direction are halted when: the cumulative alignment score falls off by the quantity X from its maximum achieved value; the cumulative score goes to zero or below, due to the accumulation of one or more negative-scoring residue alignments; or the end of either sequence is reached. The BLAST algorithm parameters W, T, and X determine the sensitivity and speed of the alignment. The BLASTN program (for nucleotide sequences) uses as defaults a word size (W) of 28, an expectation (E) of 10, M=1, N=−2, and a comparison of both strands. For amino acid sequences, the BLASTP program uses as defaults a word size (W) of 3, an expectation (E) of 10, and the BLOSUM62 scoring matrix (see Henikoff &amp; Henikoff,  Proc. Natl. Acad Sci. USA  89:10915 (1989)). 
     The BLAST algorithm also performs a statistical analysis of the similarity between two sequences (see, e.g., Karlin &amp; Altschul,  Proc. Nat&#39;L Acad Sci. USA  90:5873-5787 (1993)). One measure of similarity provided by the BLAST algorithm is the smallest sum probability (P(N)), which provides an indication of the probability by which a match between two nucleotide or amino acid sequences would occur by chance. For example, an amino acid sequence is considered similar to a reference sequence if the smallest sum probability in a comparison of the test amino acid sequence to the reference amino acid sequence is less than about 0.01, more preferably less than about 10 −5 , and most preferably less than about 10−20. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are bar graphs showing the expression levels of stable antimicrobial peptides (SAMPs) in HLB-susceptible and HLB-tolerant plants.  FIG. 1C  shows HLB-tolerant  citrus  varieties or close relatives express elevated levels of SAMPs. 
         FIGS. 2A-2C  are peptide structures showing key amino acids in the loop between two α-helixes of SAMPs. The prediction of peptide structure is performed by Swiss-model with AtSAMP1 as the template (PDB ID: 1Q4R). The sequences of CghSAMPa (also referred to as SAMPa herein) and CghSAMPb (also referred to as SAMPb herein) are shown in Table 1. 
         FIG. 3A  shows photographs of  Ca. L. solanacearum -infected  Nb  plants treated with CghSAMPa (SAMPa) or CghSAMPb (SAMPb) peptide, or mock solution. 
         FIG. 3B  shows the bacterial titers of  Ca. L. solanacearum -infected  Nb  plants treated with CghSAMPa (SAMPa) or CghSAMPb (SAMPb) peptide, or mock solution. 
         FIG. 4A-B  shows SAMP effectively suppresses the growth of C. Las ( Candidatus Liberibacter asiaticus ) in HLB-positive  citrus  plants and the new shoots have no HLB symptoms.  FIG. 4A  shows HLB-positive  citrus  plants with similar  C. Las  titer were treated with buffer (mock), or SAMP (at 100 nM or 10 μM) once by trunk injection. Pictures were taken after 5 weeks of treatment.  FIG. 4B  shows the titer of  C. Las  was measured by PCR on genomic DNA isolated from 8 new leaves from each mock or SAMP-treated  citrus  plants. 
         FIG. 5A-C  shows SAMP pre-treated potato plants grew better and produced more tubers after  C. Lso  ( Ca. L. solanacearum ) infection by potato psyllid feeding.  FIG. 5A  shows potato plants were pre-treated with SAMP (10 μM) or buffer only (mock), and then were exposed to  C. Lso  positive potato psyllids for 5 days. Plants are 3 weeks post infection.  FIG. 5B  shows potato tubers harvested from mock or SAMP pre-treated plants.  FIG. 5C  shows frying test of potato tubers harvested from SAMP or mock pre-treated  C. Lso  infected plants and healthy plants. 
         FIG. 6A-B  show SAMP pre-treated tomato plants grew better after  C. Lso  infection by potato psyllid feeding.  FIG. 6A  shows tomato plants were pre-treated with SAMP or buffer only (mock) and then were exposed to  C. Lso  positive potato psyllids for 5 days. Plants are 4 weeks post infection.  FIG. 6B  shows above-ground biomass of SAMP pre-treated tomato plants. 
         FIG. 7  shows the bacterial titers of  Ca. L. solanacearum -infected tomato plants treated with CghSAMPa or CghSAMPb peptide, or mock solution. 
         FIGS. 8A-8C  show that SAMPs have priming effect on  citrus  plants and can be used to vaccinate the seedlings in the nursery. 
         FIGS. 9A and 9B  show that SAMPs have low phytotoxic activity on  citrus  leaves. 
         FIG. 10  shows that SAMPs are highly expressed in the fruit of Australian finger lime, Australian desert lime, lemon, and  Poncirus trifoliate  (common root stock). 
         FIG. 11  shows that SAMPs are sensitive to human protease pepsin, a major gastric enzyme. 
         FIG. 12  shows that SAMPs are stable after storing at room temperature for 24 hours, or 60° C. for 24 hours, or 100° C. for 20 mins, and remain active to kill  Liberibacter crescens  as shown by the viability/cytotoxicity assay for visualizing live and dead bacterial cells (DMAO (green): a membrane-permeable DNA dye for visualizing live bacteria, and EthD-III (red): a membrane-impermeable DNA dye for visualizing dead bacteria). 
         FIG. 13  shows that SAMPs are stable in  citrus  cell lysate, which indicates that they are also stable in trees. 
         FIGS. 14A and 14B  show that SAMPs exhibit antimicrobial activity against Gram-negative bacterial pathogens  Pseudomonas syringae  and  Agrobacterium tumefaciens  in the agar diffusion assay. 
         FIG. 15  shows that SAMPs, after storage for 24 hours at 4° C., room temperature, or 60° C., remain active to kill  Agrobacterium tumefaciens  as shown by the viability/cytotoxicity assay for visualizing live and dead bacterial cells (DMAO (green): a membrane-permeable DNA dye for visualizing live bacteria and EthD-III (red): a membrane-impermeable DNA dye for visualizing dead bacteria). 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     I. Introduction 
       Citrus  greening disease or “Huanglongbing” (HLB), caused by bacteria  Candidatus Liberibacter , is a type of  Liberibacter  disease that specifically infects  citrus  plants. HLB is one of the most destructive diseases of  citrus. Liberibacter  (e.g.,  Candidatus Liberibacter  species ( Ca. Liberibacter  or  Ca. L .) or  Liberibacter crescens ) is a Gram-negative bacterial pathogen restricted to the phloem. HLB has caused in a significant reduction in  citrus  quality and quantity, resulting in billions of dollars in losses of  citrus  products every year, and seriously impacts the viability of the  citrus  industry. Current methods of treating HLB mainly involve removal of infected plants and chemical treatment against the insect vector and only led to partial control of the disease. No sustainable disease control methods for HLB have been found. The expansive and fast spread of the disease to multiple locations has already made complete removal of the infected trees an impractical strategy. 
     To identify and characterize important  citrus  defense regulators, a comparative analysis of small RNAs (sRNAs) and sRNA target genes between HLB-resistant and HLB-tolerant hybrid varieties and HLB-susceptible varieties. Several  citrus  defense regulators that uniquely respond to  Ca. L . infection in HLB-resistant and HLB-tolerant hybrid varieties, but not in HLB-susceptible varieties were identified. Among the identified  citrus  defense regulators, putative antibacterial genes encoding stable antimicrobial proteins were found to express at a much higher level in the HLB-resistant and HLB-tolerant hybrid varieties than in HLB-susceptible varieties. The HLB-resistant and HLB-tolerant hybrid rootstocks are from completely different geographic and genetic backgrounds. 
     After the identification of these stable antimicrobial proteins that provide HLB-resistance or HLB-tolerance, a functional analysis of these stable antimicrobial proteins was performed in Solanaceae plant  Nicotiana benthamiana  ( Nb ) that is infected with  Candidatus Liberibacter solanacearum  ( Ca. L. solanacearum ) transmitted by potato psyllid (Example 2). The result showed that applying SAMPs to infected plants can effectively inhibit or kill  Liberibacter  species (e.g.,  Candidatus Liberibacter  species) and achieve plant protection. 
     The disclosure includes isolated stable antimicrobial (e.g., antibacterial) peptides (SAMPs) (e.g., heat stable (HS) peptides), agricultural compositions containing such peptides, plants comprising such peptides, transgenic plants expressing such peptides, methods of using such peptides to prevent or treat bacterial diseases, such as those caused by Gram-negative bacteria, e.g., a  Liberibacter  disease (e.g., an HLB or a potato ZC disease), bacterial diseases caused by  Agrobacterium tumefaciens  (also known as  Rhizobium radiobacter ), and bacterial diseases caused by  Pseudomonas syringae , and methods of producing plants that comprise such peptides or express such peptides. The SAMPs disclosed herein can inhibit and kill bacterial pathogens, such as Gram-negative bacterial pathogens, e.g.,  Liberibacter  species,  Agrobacterium tumefaciens  (also known as  Rhizobium radiobacter ), and  Pseudomonas syringae  strains. The SAMPs disclosed herein can also provide plants with resistance or tolerance to bacterial diseases, such as those caused by Gram-negative bacteria, e.g., bacterial diseases caused by  Liberibacter  species,  Agrobacterium tumefaciens , and  Pseudomonas syringae  strains. 
     II. Stable Antimicrobial Peptides (SAMPs) 
     The disclosure provides stable antimicrobial (e.g., antibacterial) peptides (SAMPs) that may be injected into plants to prevent or treat a bacterial disease, such as a Gram-negative bacterial disease, e.g., a  Liberibacter  disease (e.g., HLB). The SAMPs disclosed herein may also be used to prevent or treat bacterial diseases caused by other bacterial pathogens, such as  Agrobacterium tumefaciens  (also known as  Rhizobium radiobacter ) and  Pseudomonas syringae  strains. The plants may also be genetically modified to express one or more of the SAMPs described herein. The present disclosure identified genes in plants encoding SAMPs that are differentially expressed in  Liberibacter  disease-resistant/tolerant (e.g., HLB-resistant/tolerant) plants and  Liberibacter  disease-susceptible (e.g., HLB-susceptible) plants. In some embodiments, the SAMPs disclosed herein are heat stable (e.g., heat stable (HS) peptides). In some embodiments, the SAMPs disclosed herein are also stable in plant extracts. In further embodiments, the SAMPs disclosed herein are also stable in plant lysates (e.g.,  citrus  lysates). As shown in  FIGS. 1A and 1B , these SAMPs expressed at a much higher level in  Liberibacter  disease-resistant/tolerant (e.g., HLB-resistant/tolerant) plants than in  Liberibacter  disease-susceptible (e.g., HLB-susceptible) plants. By comparing the amino acid sequences of SAMPs from different  citrus  plants and solanaceous plants, it is found that the SAMPs expressed in some HLB-resistant/tolerant  citrus  plants and pepper (Ca:  Capsicum annuum ) are shorter while the SAMPs expressed in HLB-susceptible solanaceous plants are longer. Table 1 below provides amino acid sequences of SAMPs in various hybrid plants,  citrus  plants, and solanaceous plants. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Plant 
                   
                   
               
               
                 SAMP 
                 Source 
                 Amino Acid Sequence 
                 Nucleic Acid Sequence 
               
               
                   
               
             
            
               
                 CghSAMPa 
                 
                   Eremocitrus 
                 
                 MCCNRGKNVSIENLHQ 
                 ATGTGCTGCAACAGGGGCAAGAATGTGAGCATTGAGA 
               
               
                   
                   glauca  x 
                 GFTHIFESTFESTEGVAE 
                 ATCTTCATCAGGGTTTCACTCATATTTTTGAATCTACC 
               
               
                   
                   citrus  sp. 
                 YVSHPSHVEYANLFLA 
                 TTTGAGAGCACAGAGGGTGTTGCAGAGTATGTATCTC 
               
               
                   
                   
                 NLEKVLVIDYKPTTVRV 
                 ATCCGTCACATGTTGAATACGCAAACTTGTTCCTGGCC 
               
               
                   
                   
                 (SEQ ID NO: 1) 
                 AACTTGGAGAAAGTTCTCGTGATTGACTACAAACCGA 
               
               
                   
                   
                   
                 CAACAGTACGTGTCTGAGAAGGGTGGGCGCGCCGACC 
               
               
                   
                   
                   
                 CAGCTTTCTTGTACAAAGTTGGCATTATAAGAAAG 
               
               
                   
                   
                   
                 (SEQ ID NO: 14) 
               
               
                   
                   
                   
                 or 
               
               
                   
                   
                   
                 ATGTGCTGCAACAGGGGCAAGAATGTGAGCATTGAGA 
               
               
                   
                   
                   
                 ATCTTCATCAGGGTTTCACTCATATTTTTGAATCTACC 
               
               
                   
                   
                   
                 TTTGAGAGCACAGAGGGTGTTGCAGAGTATGTATCTC 
               
               
                   
                   
                   
                 ATCCGTCACATGTTGAATACGCAAACTTGTTCCTGGCC 
               
               
                   
                   
                   
                 AACTTGGAGAAAGTTCTCGTGATTGACTACAAACCGA 
               
               
                   
                   
                   
                 CAACAGTACGTGTCTGA (SEQ ID NO: 28) 
               
               
                   
               
               
                 CghSAMPb 
                 
                   Eremocitrus 
                 
                 MCCNRGKNVSIENLHQ 
                 ATGTGCTGCAACAGGGGCAAGAATGTGAGCATTGAGA 
               
               
                   
                   glauca  x 
                 GFPHLFEFTFESTEGVAE 
                 ATCTTCATCAGGGTTTCCCTCATCTTTTCGAATTTACCT 
               
               
                   
                   citrus  sp. 
                 YVSHPAHVEYANLFLA 
                 TTGAGAGCACAGAGGGTGTTGCAGAGTATGTATCTCA 
               
               
                   
                   
                 NLEKVLVIDYKPTTVRV 
                 TCCGGCACATGTTGAATACGCAAACTTGTTCCTGGCC 
               
               
                   
                   
                 (SEQ ID NO: 2) 
                 AACTTGGAGAAAGTTCTCGTGATTGACTACAAACCGA 
               
               
                   
                   
                   
                 CAACAGTACGTGTCTGAGAAGGGTGGGCGCGCCGACC 
               
               
                   
                   
                   
                 CAGCTTTCTT (SEQ ID NO: 15) 
               
               
                   
                   
                   
                 or 
               
               
                   
                   
                   
                 ATGTGCTGCAACAGGGGCAAGAATGTGAGCATTGAGA 
               
               
                   
                   
                   
                 ATCTTCATCAGGGTTTCCCTCATCTTTTCGAATTTACCT 
               
               
                   
                   
                   
                 TTGAGAGCACAGAGGGTGTTGCAGAGTATGTATCTCA 
               
               
                   
                   
                   
                 TCCGGCACATGTTGAATACGCAAACTTGTTCCTGGCC 
               
               
                   
                   
                   
                 AACTTGGAGAAAGTTCTCGTGATTGACTACAAACCGA 
               
               
                   
                   
                   
                 CAACAGTACGTGTCTGA (SEQ ID NO: 29) 
               
               
                   
               
               
                 942SAMP1, 
                 
                   Citrus 
                 
                 MCCNRGKNVSIENLHQ 
                 ATGTGCTGCAACAGGGGCAAGAATGTGAGCATTGAGA 
               
               
                 US-942 
                   reticulata  x 
                 GFTHIFESTFESTEGVAE 
                 ATCTTCATCAGGGTTTCACTCATATTTTTGAATCTACC 
               
               
                   
                 
                   Poncirus 
                 
                 YVAHPAHVEYANLFLA 
                 TTTGAGAGCACAGAGGGTGTTGCAGAGTATGTAGCTC 
               
               
                   
                 
                   trifoliata 
                 
                 NLEKVLVIDYKPTTERV 
                 ATCCGGCACATGTTGAATACGCAAACTTGTTCCTGGC 
               
               
                   
                   
                 (SEQ ID NO: 3) 
                 CAACTTGGAGAAAGTTCTCGTGATTGACTACAAACCG 
               
               
                   
                   
                   
                 ACAACAGAACGTGTCTAAGGGTGGGCGCGCCGACCCA 
               
               
                   
                   
                   
                 GCTTTCTTGTACAA (SEQ ID NO: 16) 
               
               
                   
                   
                   
                 or 
               
               
                   
                   
                   
                 ATGTGCTGCAACAGGGGCAAGAATGTGAGCATTGAGA 
               
               
                   
                   
                   
                 ATCTTCATCAGGGTTTCACTCATATTTTTGAATCTACC 
               
               
                   
                   
                   
                 TTTGAGAGCACAGAGGGTGTTGCAGAGTATGTAGCTC 
               
               
                   
                   
                   
                 ATCCGGCACATGTTGAATACGCAAACTTGTTCCTGGC 
               
               
                   
                   
                   
                 CAACTTGGAGAAAGTTCTCGTGATTGACTACAAACCG 
               
               
                   
                   
                   
                 ACAACAGAACGTGTCTAA (SEQ ID NO: 30) 
               
               
                   
               
               
                 CsSAMP1 
                 
                   Citrus 
                 
                 MCCNRGKNVSIENLHQ 
                 ATGTGCTGCAACAGGGGCAAGAATGTGAGCATTGAGA 
               
               
                   
                 
                   sinensis 
                 
                 GFTHIFESTEESTEGVAE 
                 ATCTTCATCAGGGTTTCACTCATATTTTTGAATCTACC 
               
               
                   
                   
                 YVAHPAHVEYANLFLA 
                 TTTGAGAGCACAGAGGGTGTTGCAGAGTATGTAGCTC 
               
               
                   
                   
                 NLEKVLVIDYKPTTVRV 
                 ATCCGGCACATGTTGAATACGCAAACTTGTTCCTGGC 
               
               
                   
                   
                 (SEQ ID NO: 4) 
                 CAACTTGGAGAAAGTTCTCGTGATTGACTACAAACCG 
               
               
                   
                   
                   
                 ACAACAGTACGTGTCTGAGTTGTACTAGTAGGGAA 
               
               
                   
                   
                   
                 (SEQ ID NO: 17) 
               
               
                   
                   
                   
                 or 
               
               
                   
                   
                   
                 ATGTGCTGCAACAGGGGCAAGAATGTGAGCATTGAGA 
               
               
                   
                   
                   
                 ATCTTCATCAGGGTTTCACTCATATTTTTGAATCTACC 
               
               
                   
                   
                   
                 TTTGAGAGCACAGAGGGTGTTGCAGAGTATGTAGCTC 
               
               
                   
                   
                   
                 ATCCGGCACATGTTGAATACGCAAACTTGTTCCTGGC 
               
               
                   
                   
                   
                 CAACTTGGAGAAAGTTCTCGTGATTGACTACAAACCG 
               
               
                   
                   
                   
                 ACAACAGTACGTGTCTGA (SEQ ID NO: 31) 
               
               
                   
               
               
                 CsSAMP2 
                 
                   Citrus 
                 
                 MIAELIRSCCGLELLAV 
                 ATGGAAGAAGCTAAAGGAGTGGTGAAGCACGTACTTC 
               
               
                   
                 
                   sinensis 
                 
                 KYKGKNVSIENLHQGFT 
                 TGGCCAAGTTCAAAGAAGGGACTGCTCAAGATCAAAT 
               
               
                   
                   
                 HIFESTEESTEGVAEYV 
                 TGATCAGCTCATCAAAGACTATGCAAATCTTGTGAAT 
               
               
                   
                   
                 AHPAHVEYANLFLANL 
                 CTCATTGAACCCATGAAGTCTTTCCAATGGGGCAAGA 
               
               
                   
                   
                 EKVLVIDYKPTTVRV 
                 ATGTGAGCATTGAGAATCTTCATCAGGGTTTCACTCAT 
               
               
                   
                   
                 (SEQ ID NO: 5) 
                 ATTTTTGAATCTACCTTTGAGAGCACAGAGGGTGTTGC 
               
               
                   
                   
                   
                 AGAGTATGTAGCTCATCCGGCACATGTTGAATACGCA 
               
               
                   
                   
                   
                 AACTTGTTCCTGGCCAACTTGGAGAAAGTTCTCGTGAT 
               
               
                   
                   
                   
                 TGACTACAAACCGACAACAGTACGTGTCTGA (SEQ ID 
               
               
                   
                   
                   
                 NO: 18) 
               
               
                   
               
               
                 CsSAMP3 
                 
                   Citrus 
                 
                 MEEAKGVVKHVLLAKF 
                 ATGGAAGAAGCTAAAGGAGTGGTGAAGCACGTACTTC 
               
               
                   
                 
                   sinensis 
                 
                 KEGTAQDQIDQLIKDYA 
                 TGGCCAAGTTCAAAGAAGGGACTGCTCAAGATCAAAT 
               
               
                   
                   
                 NLVNLIEPMKSFQWGK 
                 TGATCAGCTCATCAAAGACTATGCAAATCTTGTGAAT 
               
               
                   
                   
                 DVSIENRHQGFTHIFEST 
                 CTCATTGAACCCATGAAGTCTTTCCAATGGGGCAAGA 
               
               
                   
                   
                 FESTEGVAEYVAHPAH 
                 ATGTGAGCATTGAGAATCTTCATCAGGGTTTCACTCAT 
               
               
                   
                   
                 VEYANLFLANLEKVLVI 
                 ATTTTTGAATCTACCTTTGAGAGCACAGAGGGTGTTGC 
               
               
                   
                   
                 DYKPTTVRV (SEQ ID 
                 AGAGTATGTAGCTCATCCGGCACATGTTGAATACGCA 
               
               
                   
                   
                 NO: 6) 
                 AACTTGTTCCTGGCCAACTTGGAGAAAGTTCTCGTGAT 
               
               
                   
                   
                   
                 TGACTACAAACCGACAACAGTACGTGTCTGA (SEQ ID 
               
               
                   
                   
                   
                 NO: 19) 
               
               
                   
               
               
                 CsSAMP4 
                 
                   Citrus 
                 
                 MGEGEEAAMGEFKHLV 
                 ATGGGTGAGGGTGAAGAGGCAGCAATGGGAGAGTTC 
               
               
                   
                 
                   sinensis 
                 
                 IVKFKEGVVVEDIVKG 
                 AAGCACTTGGTGATTGTTAAGTTCAAGGAAGGTGTGG 
               
               
                   
                   
                 MKKLVSEIDAVKSFEW 
                 TTGTGGAGGATATTGTCAAAGGGATGAAAAAGCTGGT 
               
               
                   
                   
                 GQDVEGQEMLRQGFTH 
                 TTCAGAGATTGATGCTGTCAAATCTTTTGAATGGGGCC 
               
               
                   
                   
                 AFLMTENKKEDYTTFAS 
                 AAGATGTAGAAGGGCAGGAGATGCTTAGGCAAGGCT 
               
               
                   
                   
                 HPSHVEFSATFSAAIEKI 
                 TCACACATGCATTCTTGATGACATTCAACAAGAAGGA 
               
               
                   
                   
                 VLLDFPTVLGKAPAA 
                 AGACTATACAACCTTGCAAGCCATCCCAGCCACGTC 
               
               
                   
                   
                 (SEQ ID NO: 7) 
                 GAATTCTCGGCTACATTTTCAGCTGCTATTGAGAAGAT 
               
               
                   
                   
                   
                 TGTCCTGCTTGATTTCCCTACCGTGCTTGGCAAAGCAC 
               
               
                   
                   
                   
                 CAGCAGCATGA (SEQ ID NO: 20) 
               
               
                   
               
               
                 CcSAMP1 
                 
                   Citrus 
                 
                 MKAETKGRDMEEAKG 
                 ATGAAAGCCGAAACAAAAGGCAGAGATATGGAAGAA 
               
               
                   
                 
                   clementina 
                 
                 VVKHVLLAKFKEGTAQ 
                 GCTAAAGGAGTGGTGAAGCACGTACTTCTGGCCAAGT 
               
               
                   
                   
                 DQIDQLIKDYANLVNLI 
                 TCAAAGAAGGGACTGCTCAAGATCAAATTGATCAGCT 
               
               
                   
                   
                 EPMKSFQWGKDVSIEN 
                 CATCAAAGACTATGCAAATCTTGTGAATCTCATTGAA 
               
               
                   
                   
                 LHQGFTHIFESTFESTEG 
                 CCCATGAAGTCTTTCCAATGGGGCAAGGATGTGAGCA 
               
               
                   
                   
                 VAEYVAHPAHVEYANL 
                 TTGAGAATCTTCATCAGGGTTTCACTCATATTTTTGAA 
               
               
                   
                   
                 FLANLEKVLVIDYKPTT 
                 TCTACCTTTGAGAGCACAGAGGGTGTTGCAGAGTATG 
               
               
                   
                   
                 VRV (SEQ ID NO: 8) 
                 TAGCTCATCCGGCACATGTTGAATACGCAAACTTGTTC 
               
               
                   
                   
                   
                 CTGGCCAACTTGGAGAAAGTTCTCGTGATTGACTACA 
               
               
                   
                   
                   
                 AACCGACAACTGTACGTGTCTGA (SEQ ID NO: 21) 
               
               
                   
               
               
                 CaSAMP 
                 
                   Capsicum 
                 
                 MSYGRGKDVSTENLQQ 
                 ATGTCATATGGCAGGGGTAAGGATGTGAGCACAGAG 
               
               
                   
                 
                   annuum 
                 
                 GFTHVFESTFDSTEGVA 
                 AACCTCAAGGTTTCACTCATGTTTTTGAGTCAAC 
               
               
                   
                   
                 EYVSHPVHVEFANLML 
                 GTTCGACAGTACAGAAGGTGTTGCAGAGTATGTAAGT 
               
               
                   
                   
                 PQLEKVLVIDYKPEKVG 
                 CATCCGGTTCATGTTGAATTTGCAAATCTAATGCTTCC 
               
               
                   
                   
                 P (SEQ ID NO: 9) 
                 TCAGCTGGAGAAAGTCCTCGTCATCGACTACAAACCG 
               
               
                   
                   
                   
                 GAGAAAGTCGGTCCCTAA (SEQ ID NO: 22) 
               
               
                   
               
               
                 NbSAMP 
                 
                   Nicotiana 
                 
                 MEGGKVKHILLAKFKD 
                 ATGGAGGGTGGTAAAGTGAAGCACATATTGCTGGCCA 
               
               
                   
                 
                   benthamiana 
                 
                 GIPADQIDQLIKQYANL 
                 AGTTCAAAGATGGAATTCCAGCAGACCAAATCGACCA 
               
               
                   
                   
                 VNLIEPMKAFHWGENV 
                 ACTGATTAAGCAATATGCTAATCTTGTCAATCTCATCG 
               
               
                   
                   
                 STENFHQGFTHVFESTFD 
                 AACCAATGAAAGCTTTTCATTGGGGTGAGAATGTGAG 
               
               
                   
                   
                 STEGIAEYIDHPAHVEY 
                 CATAGAGAACTTCCACCAAGGTTTCACTCATGTTTTTG 
               
               
                   
                   
                 ANTLLPQLEKVLVIDYK 
                 AGTCAACGTTCGACAGTACAGAAGGAATTGCAGAGTA 
               
               
                   
                   
                 PEKVGP (SEQ ID 
                 TATAGATCATCCGGCTCATGTTGAATATGCAAATACA 
               
               
                   
                   
                 NO: 10) 
                 TTGCTTCCTCAGCTGGAGAAAGTCCTTGTCATCGACTA 
               
               
                   
                   
                   
                 CAAACCAGAGAAAGTTGGTCCC (SEQ ID NO: 23) 
               
               
                   
                   
                   
                 or 
               
               
                   
                   
                   
                 ATGGAGGGTGGTAAAGTGAAGCACATATTGCTGGCCA 
               
               
                   
                   
                   
                 AGTTCAAAGATGGAATTCCAGCAGACCAAATCGACCA 
               
               
                   
                   
                   
                 ACTGATTAAGCAATATGCTAATCTTGTCAATCTCATCG 
               
               
                   
                   
                   
                 AACCAATGAAAGCTTTTCATTGGGGTGAGAATGTGAG 
               
               
                   
                   
                   
                 CATAGAGAACTTCCACCAAGGTTTCACTCATGTTTTTG 
               
               
                   
                   
                   
                 AGTCAACGTTCGACAGTACAGAAGGAATTGCAGAGTA 
               
               
                   
                   
                   
                 TATAGATCATCCGGCTCATGTTGAATATGCAAATACA 
               
               
                   
                   
                   
                 TTGCTTCCTCAGCTGGAGAAAGTCCTTGTCATCGACTA 
               
               
                   
                   
                   
                 CAAACCAGAGAAAGTTGGTCCCTAA (SEQ ID NO: 32) 
               
               
                   
               
               
                 SISAMP 
                 
                   Solanum 
                 
                 MEGGKGGVVKHILLAK 
                 ATGGAGGGTGGCAAAGGAGGAGTTGTGAAGCACATTT 
               
               
                   
                 
                   lycopersicum 
                 
                 FKDGIPPEQIDQLIKQYA 
                 TGCTAGCAAAGTTCAAAGATGGGATCCCACCTGAACA 
               
               
                   
                   
                 NLVNLVEPMKAFQWG 
                 GATTGATCAACTCATTAAGCAGTATGCTAATCTTGTCA 
               
               
                   
                   
                 KDVSIENLHQGFTHVFE 
                 ATCTTGTTGAACCCATGAAGGCTTTTCAATGGGGTAA 
               
               
                   
                   
                 STFDSLEGVAEYIAHPV 
                 GGATGTGAGCATAGAAAATCTTCATCAAGGTTTCACT 
               
               
                   
                   
                 HVEYANTLLPQLEKFLI 
                 CATGTTTTCGAGTCTACGTTTGACAGTTTAGAAGGTGT 
               
               
                   
                   
                 VDYKPQ (SEQ ID 
                 TGCAGAGTATATAGCTCATCCTGTTCATGTTGAATATG 
               
               
                   
                   
                 NO: 11) 
                 CAAATACATTGCTTCCTCAGCTGGAGAAATTCCTTATC 
               
               
                   
                   
                   
                 GTCGACTACAAACCACAG (SEQ ID NO: 24) 
               
               
                   
                   
                   
                 or 
               
               
                   
                   
                   
                 ATGGAGGGTGGCAAAGGAGGAGTTGTGAAGCACATTT 
               
               
                   
                   
                   
                 TGCTAGCAAAGTTCAAAGATGGGATCCCACCTGAACA 
               
               
                   
                   
                   
                 GATTGATCAACTCATTAAGCAGTATGCTAATCTTGTCA 
               
               
                   
                   
                   
                 ATCTTGTTGAACCCATGAAGGCTTTTCAATCTGGGTAA 
               
               
                   
                   
                   
                 GGATGTGAGCATAGAAAATCTTCATCAAGGTTTCACT 
               
               
                   
                   
                   
                 CATGTTTTCGAGTCTACGTTTGACAGTTTAGAAGGTGT 
               
               
                   
                   
                   
                 TGCAGAGTATATAGCTCATCCTGTTCATGTTGAATATG 
               
               
                   
                   
                   
                 CAAATACATTGCTTCCTCAGCTGGAGAAATTCCTTATC 
               
               
                   
                   
                   
                 GTCGACTACAAACCACAGTAA (SEQ ID NO: 33) 
               
               
                   
               
               
                 SmSAMP 
                 
                   Solanum 
                 
                 MNIAVFLPSSCPALPRS 
                 ATGAATATTGCTGTCTTTCTCCCTTCGTCCTGCCCTGC 
               
               
                   
                 
                   melongena 
                 
                 KASRPSPPGQFPFLAKN 
                 CCTGCCCCGCTCAAAGGCTTCCCGCCCATCCCCACCCG 
               
               
                   
                   
                 VQLLLVLRSYSSTARA 
                 GCCAATTTCCGTTCCTAGCCAAGAATGTTCAGCTTCTA 
               
               
                   
                   
                 MSLRGENVSIENLHQGF 
                 CTAGTCTTGAGGTCTTATAGTTCCACCGCTCGTGCTAT 
               
               
                   
                   
                 THVFESTFDSVEGIAEYI 
                 GTCACTTAGGGGTGAGAATGTGAGCATAGAGAACCTC 
               
               
                   
                   
                 DHPAHVEYANILLTQLE 
                 CACCAAGGTTTCACTCACGTTTTCGAGTCAACGTTTGA 
               
               
                   
                   
                 KVLVIDYKPEKLSP 
                 CAGTGTAGAAGGCATTGCAGAGTATATAGATCATCCT 
               
               
                   
                   
                 (SEQ ID NO: 12) 
                 GCTCATGTTGAATATGCAAATATATTGCTTACTCAGCT 
               
               
                   
                   
                   
                 GGAGAAAGTCCTTGTCATCGACTACAAACCAGAGAAA 
               
               
                   
                   
                   
                 CTCAGCCCCTAA (SEQ ID NO: 25) 
               
               
                   
               
               
                 StSAMP 
                 
                   Solanum 
                 
                 MEGGKGGVVKHILLAK 
                 CTCATACAATCAACCAAATAAAGGACCCTTTTCTCTCC 
               
               
                   
                 
                   tuberosum 
                 
                 FKDGIPPEQIDQLIKQYA 
                 ACTATTTTTGCTTGTCTAGTCAAGGAAGAAGAGTGAT 
               
               
                   
                   
                 NLVNLIEPMKAFQWGK 
                 AAAATAGAAATGGAGGGTGGTAAAGGAGGAGTGGTG 
               
               
                   
                   
                 DVSIENLHQGFTHVFES 
                 AAGCACATTTTGCTAGCAAAGTTCAAAGATGGGATCC 
               
               
                   
                   
                 TFDSLEGVAEYIAHPVH 
                 CACCTGAACAAATTGATCAACTCATTAAGCAGTATGC 
               
               
                   
                   
                 VEFANTMLPQLEKVLII 
                 TAATCTTGTCAATCTTATTGAACCCATGAAGGCTTTTC 
               
               
                   
                   
                 DYKPQ (SEQ ID 
                 AATGGGGCAAGGATGTGAGCATAGAAAACCTTCACCA 
               
               
                   
                   
                 NO: 13) 
                 AGGTTTCACTCATGTTTTTGAGTCGACGTTTGACAGTT 
               
               
                   
                   
                   
                 TAGAAGGCGTTGCAGAGTATATAGCTCATCCTGTTCA 
               
               
                   
                   
                   
                 TGTFGAATTTGCAAATACAATGCTTCCTCAGCTGGAG 
               
               
                   
                   
                   
                 AAAGTCCTTATCATTGACTACAAACCACAGTAACTCA 
               
               
                   
                   
                   
                 GTCCCTAAACTGGATTCACAAATTGATGCACTTGATGT 
               
               
                   
                   
                   
                 AATAGGTATATCAGTTTTACTTTACTGTACTGAAATCC 
               
               
                   
                   
                   
                 AATAAGAACACAAACTTTTATTAAGGGTGTGTGTCTT 
               
               
                   
                   
                   
                 GCTTGTTTGCAATTATTGTATTCACTTCGTAGACGCTA 
               
               
                   
                   
                   
                 ATGCGAGTAACTTATGGTCAGCTTGGGCTGTTTAAACT 
               
               
                   
                   
                   
                 CGAGGAAGAATGCTCTTCGTTCTTCTCTTCCCAGGGAG 
               
               
                   
                   
                   
                 AATGAATGATGAACAACATATAAGTGCATCAATAAAC 
               
               
                   
                   
                   
                 TCAGATTGGTGTTTCCATTTCCT (SEQ ID NO: 26) 
               
               
                   
                   
                   
                 or 
               
               
                   
                   
                   
                 ATGGAGGGTGGTAAAGGAGGAGTGGTGAAGCACATT 
               
               
                   
                   
                   
                 TTGCTAGCAAAGTTCAAAGATGGGATCCCACCTGAAC 
               
               
                   
                   
                   
                 AAATTGATCAACTCATTAAGCAGTATGCTAATCTTGTC 
               
               
                   
                   
                   
                 AATCTTATTGAACCCATGAAGGCTTTTCAATGGGGCA 
               
               
                   
                   
                   
                 AGGATGTGAGCATAGAAAACCTTCACCAAGGTTTCAC 
               
               
                   
                   
                   
                 TCATGTTTTTGAGTCGACGTTTGACAGTTTAGAAGGCG 
               
               
                   
                   
                   
                 TTGCAGAGTATATAGCTCATCCTGTTCATGTTGAATTT 
               
               
                   
                   
                   
                 GCAAATACAATGCTTCCTCAGCTGGAGAAAGTCCTTA 
               
               
                   
                   
                   
                 TCATTGACTACAAACCACAGTAA (SEQ ID NO: 34) 
               
               
                   
               
               
                 PtSAMP1a 
                 
                   Ponirus 
                 
                 MCCNRGKNVSIENLHQ 
                 ATGTGCTGCAACAGGGGCAAGAATGTGAGCATTGAGA 
               
               
                   
                 
                   trifoliata 
                 
                 GFTHIFESTFESTEGVAE 
                 ATCTTCATCAGGGTTTCACTCATATTTTTGAATCTACC 
               
               
                   
                   
                 YVAHPAHVEYANSFLA 
                 TTTGAGAGCACAGAGGGTGTTGCAGAGTATGTAGCTC 
               
               
                   
                   
                 NLEKVLVIDYKPTTVRV 
                 ATCCGGCACATGTTGAATACGCAAACTCGTTCCTGGC 
               
               
                   
                   
                 (SEQ ID NO: 35) 
                 CAACTTGGAGAAAGTTCTCGTGATTGACTACAAACCG 
               
               
                   
                   
                   
                 ACAACAGTACGTGTCTGA (SEQ ID NO: 38) 
               
               
                   
               
               
                 PtSAMP1b 
                 
                   Ponirus 
                 
                 MCCNRGKNVSIENLHQ 
                 ATGTGCTGCAACAGGGGCAAGAATGTGAGCATTGAGA 
               
               
                   
                 
                   trifoliata 
                 
                 GFTHIFESTFESTEGVAE 
                 ATCTTCATCAGGGTTTCACTCATATTTTTGAATCTACC 
               
               
                   
                   
                 YVAHPAHVEYTNSFLA 
                 TTTGAGAGCACAGAGGGTGTTGCAGAGTATGTAGCTC 
               
               
                   
                   
                 NLEKVLVIDYKPTTVRV 
                 ATCCGGCACATGTTGAATACACAAACTCGTTCCTGGC 
               
               
                   
                   
                 (SEQ ID NO: 36) 
                 CAACTTGGAGAAAGTTCTCGTGATTGACTACAAACCG 
               
               
                   
                   
                   
                 ACAACAGTACGTGTCTGA (SEQ ID NO: 39) 
               
               
                   
               
               
                 MCaSAMP 
                 
                   Microcitrus 
                 
                 MCCNRGKNVSIENLHQ 
                 ATGTGCTGCAACAGGGGCAAGAATGTGAGTATTGAGA 
               
               
                   
                 
                   australasica 
                 
                 GFTHIFESTFESTEGVAE 
                 ATCTTCATCAGGGTTTCACTCATATTTTTGAATCTACC 
               
               
                   
                   
                 YVSHPAHVEYANLFLA 
                 TTTGAGAGCACAGAGGGTGTTGCAGAGTATGTATCTC 
               
               
                   
                   
                 NLEKVLVIDYKPTTVRV 
                 ATCCGGCACATGTTGAATACGCAAACTTGTTCCTCGCC 
               
               
                   
                   
                 (SEQ ID NO: 37) 
                 AACTTGGAGAAAGTTCTCGTGATTGACTACAAACCGA 
               
               
                   
                   
                   
                 CAACAGTACGTGTCTGA (SEQ ID NO: 40) 
               
               
                   
               
            
           
         
       
     
     Further, SAMPs (e.g., HS peptides) from the  Liberibacter  disease-resistant/tolerant (e.g., HLB-resistant/tolerant) plants contain a few different amino acids within the α-β barrel domain as compared to the corresponding amino acids in the  Liberibacter  disease-susceptible (e.g., HLB-susceptible) plants. Two key amino acid differences between the  Liberibacter  disease-resistant/tolerant (e.g., HLB-resistant/tolerant) plants and the  Liberibacter  disease-susceptible (e.g., HLB-susceptible) plants are identified in the loop between two α-helixes of SAMPs ( FIGS. 2A-2C ). These two amino acid positions are indicated as bold and underlined in the sequence alignment of SEQ ID NOs:1-13 and 35-37. 
     
       
         
           
               
               
               
            
               
                 CghSAMPa 
                 -------------------------------------------MCC------------NR 5 
                   
               
               
                   
               
               
                 CghSAMPb 
                 -------------------------------------------MCC------------NR 5 
               
               
                   
               
               
                 942SAMP1 
                 -------------------------------------------MCC------------NR 5 
               
               
                   
               
               
                 CsSAMP1 
                 -------------------------------------------MCC------------NR 5 
               
               
                   
               
               
                 CsSAMP2 
                 ------------------------------------MIAELIRSCC----GLELLAVKYK 20 
               
               
                   
               
               
                 CsSAMP3 
                 ---------MEEAKGVVKHVILAKETEGTAQDQIDQLIKDYANLVN----LIEPMKSFQW 47 
               
               
                   
               
               
                 CsSAMP4 
                 -----MGEGEEAAMGEFKHLVIVKFKEGVVVEDIVKGMK---KLVS----EIDAVKSFEW 48 
               
               
                   
               
               
                 CcSA11P1 
                 MKAETKGRDMEEAKGVVKHVLLAKFKEGTAQDQIDQLIKDYANLVN----LIEPMKSFQW 56 
               
               
                   
               
               
                 CaSANP 
                 -------------------------------------------------------MSYGR 5 
               
               
                   
               
               
                 NbSAMP 
                 -----------MEGGKVKHILLAKFKDGIPADQIDQLIKQYANLVN----LIEPMKAFHW 45 
               
               
                   
               
               
                 S1SANP 
                 --------MEGGKGGVVKHILLAKFKDGIPPEQIDQLIKQYANLVN----LVEPMKAFQW 48 
               
               
                   
               
               
                 SmSAMP 
                 MNIAV------FLPSSCPALPRSKASRPSPPGQFPFLAKNVQLLLVLRSYSSTARAMSLR 54 
               
               
                   
               
               
                 StSAMP 
                 --------MEGGKGGVVKHILLAKFKDGIPPEQIDQLIKQYANLVN----LIEPMKAFQW 48 
               
               
                   
               
               
                 PtSANP1a 
                 -------------------------------------------MCC------------NR 5 
               
               
                   
               
               
                 PtSAMP1b 
                 -------------------------------------------MCC------------NR 5 
               
               
                   
               
               
                 MCaSAMP 
                 -------------------------------------------MCC------------NR 5 
               
               
                   
               
               
                 CghSAMPa 
                 GKNVSI-ENLHQGFTHIFESTFESTEGVAEYV S HP S HVEYANLFLANLEKVLVIDYKPTT 64 
               
               
                   
               
               
                 CghSAMPb 
                 GKNVSI-ENLHQGFPHLFEFTFESTEGVAEYV S HP A HVEYANLFLANLEKVLVIDYKPTT 64 
               
               
                   
               
               
                 942SAMP1 
                 GKNVSI-ENLHQGFTHIFESTFESTEGVAEYV A HP A HVEYANLFLANLEKVLVIDYKPTT 64 
               
               
                   
               
               
                 CsSANP1 
                 GKNVSI-ENLHQGFTHIFESTFESTEGVAEYN A HP A HVEYANLFLANLEKVLVIDYKPTT 64 
               
               
                   
               
               
                 CsSAMP2 
                 GKNVSI-ENLHQGFTHIFESTFESTEGVAEYV A HP A HVEYANLFLANLEKVLVIDYKPTT 79 
               
               
                   
               
               
                 CsSAMP3 
                 GKDVSI-ENRHQGFTHIFESTFESTEGVAEYV A HP A HVEYANLFLANLEKVLVIDYKPTT 106 
               
               
                   
               
               
                 CsSAMP4 
                 GQDVEGQEMLRQGFTHAFLMTFNKKEDYTTFA S HP S HVEFSATFSAAIEKIVLLDFPTVL 108 
               
               
                   
               
               
                 CcSAMP1 
                 GKDVSI-ENLHQGFTHIFESTFESTEGVAEYV A HP A HVEYANLFLANLEKVLVIDYKPTT 115 
               
               
                   
               
               
                 CaSAMP 
                 GKDVST-ENLQQGFTHVFESTFDSTEGVAEYV S HP V HVEFANLMLPQLEKVLVIDYKPEK 64 
               
               
                   
               
               
                 NbSAMP 
                 GENVSI-ENFHQGFTHVFESTFDSTEGIAEYI D HP A HVEYANTLLPQLEKVLVIDYKPEK 104 
               
               
                   
               
               
                 SlSANP 
                 GKDVSI-ENLHQGFTHVFESTFDSLEGVAEYI A HP V HVEYANTLLPQLEKFLIVDYKPQ- 106 
               
               
                   
               
               
                 SmSAMP 
                 GENVSI-ENLHQGFTHVFESTFDSVEGIAEYI D HP A HVEYANILLTQLEKVLVIDYKPEK 113 
               
               
                   
               
               
                 StSAMP 
                 GKDVSI-ENLHQGFTHVFESTFDSLEGVAEYI A HP V HVEFANTMLPQLEKVLIIDYKPQ- 106 
               
               
                   
               
               
                 PtSAMP1a 
                 GKNVSI-ENLHQGFTHIFESTFESTEGVAEYV A HP A HVEYANSFLANLEKVLVIDYKPTT 64 
               
               
                   
               
               
                 PtSAMP1b 
                 GKNVSI-ENLHQGFTHIFESTFESTEGVAEYV A HP A HVEYTNSFLANLEKVLVIDYKPTT 64 
               
               
                   
               
               
                 MCaSAMP 
                 GKNVSI-ENLHQGFTHIFESTFESTEGVAEYV S HP A HVEYANLFLANLEKVLVIDYKPTT 64 
               
               
                   
                 *::*.  *  :*** * *  **:. *. : :  ** ***::  :   :**.:::*: 
               
               
                   
               
               
                 CghSAMPa 
                 VRV--- 67 
               
               
                   
               
               
                 CghSAMPb 
                 VRV--- 67 
               
               
                   
               
               
                 9428AMP1 
                 ERV--- 67 
               
               
                   
               
               
                 CsSAMP1 
                 VRV--- 67 
               
               
                   
               
               
                 CsSAMP2 
                 VRV--- 82 
               
               
                   
               
               
                 CsSAMP3 
                 VRV--- 109 
               
               
                   
               
               
                 CsSAMP4 
                 GKAPAA 114 
               
               
                   
               
               
                 CcSAMP1 
                 VRV--- 118 
               
               
                   
               
               
                 CaSAMP 
                 VGP--- 67 
               
               
                   
               
               
                 NbSAMP 
                 VGP--- 107 
               
               
                   
               
               
                 SlSAMP 
                 ------ 106 
               
               
                   
               
               
                 SmSAMP 
                 LSP--- 116 
               
               
                   
               
               
                 StSAMP 
                 ------ 106 
               
               
                   
               
               
                 PtSAMP1a 
                 VRV--- 67 
               
               
                   
               
               
                 PtSAMP1b 
                 VRV--- 67 
               
               
                   
               
               
                 MCaSAMP 
                 VRV--- 67 
               
            
           
         
       
     
     In particular, SAMPs disclosed herein include the following: 
     
       
         
           
               
            
               
                   Poncirus trifoliata  Flying Dragon 1, 
               
               
                 Kryder 55-5, Nanjing 
               
               
                 (SEQ ID NO: 35) 
               
               
                 MCCNRGKNVSIENLHQGFTHIFESTFESTEGVAEYVAHPAHVEYANSFL 
               
               
                   
               
               
                 ANLEKVLVIDYKPTTVRV 
               
               
                   
               
               
                   Poncirus trifoliata  Flying Dragon 2 
               
               
                 (SEQ ID NO: 36) 
               
               
                 MCCNRGKNVSIENLHQGFTHIFESTFESTEGVAEYVAHPAHVEYTNSFL 
               
               
                   
               
               
                 ANLEKVLVIDYKPTTVRV 
               
               
                   
               
               
                   Microcitrus australasica  and  Poncirus   
               
               
                   trifoliate  (Texas): 
               
               
                 (SEQ ID NO: 37) 
               
               
                 MCCNRGKNVSIENLHQGFTHIFESTFESTEGVAEYVSHPAHVEYANLFL 
               
               
                   
               
               
                 ANLEKVLVIDYKPTTVRV 
               
               
                   
               
               
                 Australian desert lime  Eremocitrus glauca  1 
               
               
                 (SEQ ID NO: 1) 
               
               
                 MCCNRGKNVSIENLHQGFTHIFESTFESTEGVAEYVSHPSHVEYANLFL 
               
               
                   
               
               
                 ANLEKVLVIDYKPTTVRV 
               
            
           
         
       
     
     The present disclosure provides isolated stable antimicrobial (e.g., antibacterial) peptides (SAMPs) (e.g., HS peptides) comprising a sequence that is substantially identical (e.g., at least 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94% 95%, 96%, 97%, 98%, or 99% identical to) to a sequence of any one of SEQ ID NOs:1-13 and 35-37 (e.g., SEQ ID NOs:1-5 and 9). In some embodiments, the isolated peptides comprise a sequence having at least 75% sequence identity (e.g., at least 80%, 85%, 90%, 91%, 92%, 93%, 94% 95%, 96%, 97%, 98%, or 99% sequence identity) to a sequence of any one of SEQ ID NOs:1-13 and 35-37 (e.g., SEQ ID NOs:1-5 and 9). In particular embodiments, the isolated peptides comprise a sequence having at least 75% sequence identity (e.g., at least 80%, 85%, 90%, 91%, 92%, 93%, 94% 95%, 96%, 97%, 98%, or 99% sequence identity) to a sequence of any one of SEQ ID NOs:1 and 2. 
     The present disclosure provides isolated SAMPs (e.g., HS peptides) comprising a sequence having at least one amino acid substitution (e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 amino acid substitutions) relative to a sequence of any one of SEQ ID NOs:1-13 and 35-37 (e.g., SEQ ID NOs: 1-5 and 9). In particular embodiments, the isolated peptides comprise a sequence having at least one amino acid substitution (e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 amino acid substitutions) relative to a sequence of any one of SEQ ID NOs:1 and 2. 
     Isolated SAMPs (e.g., HS peptides) of the present disclosure may also comprise a sequence of 
     X 1 GX 2 X 3 VSX 4 ENX 5 X 6 QGFX 7 HX 8 FEX 9 TFX 10 SX 11 EGX 12 AEYX 13 X 14 HPX 15 HVEX 16 ANX 17  X 18 LX 19 X 20 LEKX 21 LX 22 X 23 DYKPX 24 TX 25 RV (SEQ ID NO:27), in which X 1  is R, K, or W; X 2  is K or E; X 3  is N or D; X 4  is T or I; X 5  is L, F, or R; X 6  is H or Q; X 7  is P or T; X 8  is I, L, or V; X 9  is S or F; X 10  is E or D; X 11  is T or L; X 12  is V or I; X 13  is V or I; X 14  is S, A, or D; X 15  is S, A, or V; X 16  is Y or F; X 17  is L or T; X 18  is F, M, or L; X 19  is A, P, or T; X 20  is N or Q; X 21  is V or F; X 22  is V or I; X 23  is V or I; X 24  is T, E, or Q; and X 25  is V, E, L. In particular embodiments of isolated SAMPs (e.g., HS peptides) comprising a sequence of SEQ ID NO:27, X 1  may be R; X 2  may be K; X 3  may be N; X 4  may be I; X 5  may be L; X 6  may be H; X 10  may be E; X 11  may be T; X 12  may be V; X 13  may be V; X 16  may be Y; X 17  may be L; X 18  may be F; X 19  may be A; X 20  may be N; X 21  may be V; X 22  may be V, X 23  may be I; and/or X 24  may be T. 
     In certain embodiments, the disclosure also provides methods of producing a plant (e.g., a  citrus  plant) having enhanced  Liberibacter  disease resistance (e.g., HLB resistance) or  Liberibacter  disease tolerance (e.g., HLB tolerance) (i.e., enhanced resistance or tolerance to a bacterial infection caused by bacteria in the genus  Liberibacter  (e.g.,  Candidatus Liberibacter  species) or  Liberibacter crescens ) by introducing a mutation into a polynucleotide in the plant, in which the mutated polynucleotide encodes a SAMP of the present disclosure, such as the SAMPs described above (e.g., SAMPs having at least 75% sequence identity (e.g., at least 80%, 85%, 90%, 91%, 92%, 93%, 94% 95%, 96%, 97%, 98%, or 99% sequence identity) or at least one amino acid substitution (e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 amino acid substitutions) relative to the sequence of any one of SEQ ID NOs:1-13 and 35-37 (e.g., SEQ ID NOs: 1-5 and 9). In particular, the mutated polynucleotide may encode a SAMP having at least 75% sequence identity (e.g., at least 80%, 85%, 90%, 91%, 92%, 93%, 94% 95%, 96%, 97%, 98%, or 99% sequence identity) or at least one amino acid substitution (e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 amino acid substitutions) relative to the sequence of any one of SEQ ID NOs:1 and 2. 
     In other embodiments, methods of producing a plant (e.g., a  citrus  plant) having enhanced  Liberibacter  disease resistance (e.g., HLB resistance) or  Liberibacter  disease tolerance (e.g., HLB tolerance) (i.e., enhanced resistance or tolerance to a bacterial infection caused by bacteria in the genus  Liberibacter  (e.g.,  Candidatus Liberibacter  species) or  Liberibacter crescens ) may be achieved by introducing one or more mutations into a polynucleotide in the plant, in which the mutations specifically alter the amino acids in the native SAMP in the plant that correspond to the two bold and underlined amino acids in the sequence alignment shown above. For example, the positions in a polynucleotide sequence encoding a native SAMP in a plant that correspond to the two bold and underlined amino acids in the sequence alignment shown above may be mutated to encode S, A, or D as the first of two bold and underlined amino acids and S, A, or V as the second of the two bold and underlined amino acids. 
     In some embodiments, one of skill in the art may perform sequence alignment of a polynucleotide sequence encoding a native SAMP in a plant and a polynucleotide sequence encoding an effective SAMP (e.g., SEQ ID NO: 14 or 15) to determine specific nucleic acids in the polynucleotide of the plant that need to be mutated such that the resulting mutated polynucleotide in the plant encodes the substantially the same polynucleotide sequence as that of an effective SAMP (e.g., SEQ ID NO: 14 or 15). 
     The disclosure also provides methods of preventing or treating a  Liberibacter  disease (e.g., HLB) and/or preventing or treating a bacterial infection caused by bacteria in the genus  Liberibacter  (e.g.,  Candidatus Liberibacter  species or  Liberibacter crescens ) in a plant by contacting the plant with a SAMP described above (e.g., SAMPs having at least 75% sequence identity to or at least one amino acid substitution relative to the sequence of any one of SEQ ID NOs:1-13 and 35-37 (e.g., SEQ ID NOs:1-5 and 9 (e.g., SEQ ID NOT and 2)). Without being bound by any theory, SAMPs (e.g., HS peptides) may target and destroy bacterial cells, and/or induce defense response in plants, thus, enhancing the  Liberibacter  disease resistance or  Liberibacter  disease tolerance of plants. An example of a bacterial infection caused by bacteria in the genus  Liberibacter  (e.g.,  Candidatus Liberibacter  species or  Liberibacter crescens ) that can be treated or prevented as described herein is potato zebra chip disease. For example, potato zebra disease can be treated or prevented in potato or tomato plants. 
     III. Agricultural Compositions 
     The disclosure also provides agricultural compositions that contain one or more of the SAMPs (e.g., HS peptides) described herein for use in preventing or treating a bacterial disease (e.g., a  Liberibacter  disease (HLB) or potato Zebra Chip disease, and other bacterial diseases such as those caused by  Agrobacterium tumefaciens  (also known as  Rhizobium radiobacter ) and  Pseudomonas syringae ) in a plant. In some embodiments, the agricultural composition further includes at least one of an herbicide, an herbicide safener, a surfactant, a fungicide, a pesticide, a nematicide, a plant activator, a synergist, a plant growth regulator, an insect repellant, an acaricide, a molluscicide, or a fertilizer. 
     An agricultural composition comprising one or more SAMPs (e.g., HS peptides) described herein can also include one or more of: a surface-active agent, an inert carrier, a preservative, a humectant, a feeding stimulant, an attractant, an encapsulating agent, a binder, an emulsifier, a dye, a UV protective, a buffer, a flow agent, a fertilizer, a nitrogen fixation agent, micronutrient donors, or other preparations that influence plant growth. The agricultural composition can also include one or more agrochemicals including: herbicides, insecticides, fungicides, bactericides, nematicides, molluscicides, acaracides, plant growth regulators, harvest aids, and fertilizers, which can also be combined with carriers, surfactants or adjuvants as appropriate for the agrochemical. Suitable carriers and adjuvants can be solid or liquid and correspond to the substances ordinarily employed in formulation technology, e.g., natural or regenerated mineral substances, solvents, dispersants, wetting agents, tackifiers, binders, or fertilizers. The active ingredients of the present disclosure are normally applied in the form of compositions and can be applied to the crop area, plant, or seed to be treated. For example, the compositions of the present disclosure may be applied during growth, seeding, or storage. 
     Surface-active agents that can be used with the presently described SAMPs (e.g., HS peptides) include anionic compounds such as a carboxylate of, for example, a metal; carboxylate of a long chain fatty acid; an N-acylsarcosinate; mono- or di-esters of phosphoric acid with fatty alcohol ethoxylates or salts of such esters; fatty alcohol sulfates such as sodium dodecyl sulfate, sodium octadecyl sulfate or sodium cetyl sulfate; ethoxylated fatty alcohol sulfates; ethoxylated alkylphenol sulfates; lignin sulfonates; petroleum sulfonates; alkyl aryl sulfonates such as alkyl-benzene sulfonates or lower alkylnaphtalene sulfonates, e.g., butyl-naphthalene sulfonate; salts of sulfonated naphthalene-formaldehyde condensates; salts of sulfonated phenol-formaldehyde condensates; more complex sulfonates such as the amide sulfonates, e.g., the sulfonated condensation product of oleic acid and N-methyl taurine; or the dialkyl sulfosuccinates, e.g., the sodium sulfonate or dioctyl succinate. Non-ionic agents include condensation products of fatty acid esters, fatty alcohols, fatty acid amides or fatty-alkyl- or alkenyl-substituted phenols with ethylene oxide, fatty esters of polyhydric alcohol ethers, e.g., sorbitan fatty acid esters, condensation products of such esters with ethylene oxide, e.g., polyoxyethylene sorbitar fatty acid esters, block copolymers of ethylene oxide and propylene oxide, acetylenic glycols such as 2,4,7,9-tetraethyl-5-decyn-4,7-diol, or ethoxylated acetylenic glycols. Examples of a cationic surface-active agent include, for instance, an aliphatic mono-, di-, or polyamine such as an acetate, naphthenate or oleate; or oxygen-containing amine such as an amine oxide of polyoxyethylene alkylamine; an amide-linked amine prepared by the condensation of a carboxylic acid with a di- or polyamine; or a quaternary ammonium salt. 
     Examples of inert materials or inert carriers that can be used include, but are not limited to, inorganic minerals such as kaolin, phyllosilicates, carbonates, sulfates, phosphates, or botanical materials such as cork, powdered corncobs, peanut hulls, rice hulls, and walnut shells. 
     Herbicides that can be used with the presently described SAMPs (e.g., HS peptides) include compounds that kill or inhibit growth or replication of undesired plants, typically a subset of plants that is distinct from the desired plant or crop. There are several modes of action: ACCase inhibition, carotenoid biosynthesis inhibition, cell wall synthesis inhibition, ALS inhibition, ESP synthase inhibition, glutamine synthase inhibition, HPPD inhibition, microtubule assembly inhibition, PPO inhibition, etc. Examples of commercially available herbicides include One-Time®, MSMA, Corvus®, Volunteer®, Escalade®, Q4®, Raptor®, Acumen®, Sencor®, Bullet®, TopNotch®, Valor®, PastureGard®, glycophosate (Roundup®), DSMA, Break-Up®, Hyvar®, Barricade®, etc. Herbicides can be mixed with “herbicide safeners” to reduce general toxicity of the herbicide, as described, e.g., in Riechers et al. (2010)  Plant Physiol.  153:3. 
     Pesticides (e.g., nematicides, molluscicides, insecticides, miticide/acaricides) can be used in combination with the presently disclosed SAMPs (e.g., HS peptides) to kill or reduce the population of undesirable pests affecting the plant. Pesticides can also be used with repellants or pheromones to disrupt mating behavior. Insectides are directed to insects, and include, e.g., those of botanical origin (e.g., allicin, nicotine, oxymatrine, jasmolin I and II, quassia, rhodojaponin III, and limonene), carbamate insecticides (e.g., carbaryl, carbofuran, carbosulfan, oxamyl, nitrilacarb, CPMC, EMPC, fenobucarb), fluorine insecticides, formamidine insecticides, fumigants (e.g., ethylene oxide, methyl bromide, carbon disulfide), chitin synthesis inhibitors, macrocyclic lactone insecticides, neonicotinoid insecticides, organophosphate insectides, urea and thiourea insectides, etc. Nematicides affect nematodes, and include, e.g., organophosphorus nematicides (e.g., diamidafos, fosthiazate, heterophos, phsphamidon, triazophos), fumigant nematicides (e.g., carbon disulfide, methyl bromide, methyl iodide), abamectin, carvacrol, carbamate nematicides (e.g., benomyl, oxamyl), etc. Molluscicides are directed to slugs and snails, and include, e.g., allicin, bromoacetamide, thiocarb, trifenmorph, fentin, copper sulfate, etc. Many pesticides target more than one type of pest, so that one or two can be selected to target insects, mollusks, nematodes, mitogens, etc. 
     Fertilizers typically provide macro- and micronutrients in a form that they can be utilized by the plant, or a plant-associated organism. These include, e.g., nitrogen, phosphorus, potassium, sulfur, calcium, potassium, boron, chlorine, copper, iron, manganese, molybdenum, zinc, nickel, and selenium. Fertilizers are often tailored to specific soil conditions or for particular crops or plants. Fertilizers that can be used include naturally-occurring, modified, concentrated and/or chemically synthesized materials, e.g., manure, bone meal, compost, fish meal, wood chips, etc., or can be chemically synthesized, UAN, anhydrous ammonium nitrate, urea, potash, etc. Suppliers include Scott®, SureCrop®, BCF®, RVR®, Gardenline®, and many others known in the art. 
     Fungicides are compounds that can kill fungi or inhibit fungal growth or replication. Fungicides that can be used with the presently disclosed SAMPs (e.g., HS peptides) include contact, translaminar, and systemic fungicides. Examples include sulfur, neem oil, rosemary oil, jojoba, tea tree oil,  Bacillus subtilis , Ulocladium, cinnamaldehyde, etc. 
     The agricultural compositions of the disclosure can be in a suitable form for direct application or as a concentrate of primary composition that requires dilution with a suitable quantity of water or other diluent before application. The concentration of the SAMP (e.g., an HS peptide) in the agricultural composition will vary depending upon the nature of the particular formulation, specifically, whether it is a concentrate or to be used directly, the type of plant, and in some cases, on the nature of the use, e.g., for preventing a plant that is at risk of a  Liberibacter  disease (e.g., HLB) or for treating a plant that is already infected with a  Liberibacter  disease (e.g., HLB). 
     IV. Methods of Preventing or Treating a Bacterial Disease 
     As described herein, SAMPs may be used to prevent or treat a bacterial disease, e.g., a Gram-negative bacterial disease. A  Liberibacter  disease refers to an infection caused by Gram-negative bacteria in the genus  Liberibacter  (e.g.,  Candidatus Liberibacter  species or  Liberibacter crescens ). A  Liberibacter  disease may infect plants such as  citrus  plants (e.g., orange, grapefruit, tangerine, lemon, line, key line, papeda, citron, and pomelo) and solanaceous plants (e.g., potato, tomato, eggplant, and pepper). Huanglongbing (HLB) is a type of  Liberibacter  disease that infects  citrus  plants. Potato Zebra Chip (ZC) disease is a type of  Liberibacter  disease that infects potato plants. The infection is vectored and transmitted by potato psyllids (e.g.,  Bactericera cockerelli ). The methods of utilizing the SAMPs disclosed herein may also be used to prevent or treat other bacterial diseases (e.g., other Gram-negative bacterial diseases), such as those caused by  Agrobacterium tumefaciens  (also known as  Rhizobium radiobacter ) and  Pseudomonas syringae.    
     HLB 
     The present disclosure also provides methods of preventing or treating HLB in plants. In some embodiments of the methods, the plants with HLB may be contacted with a SAMPs (e.g., an HS peptide) described herein (e.g., a SAMP comprising at least 75% sequence identity to the sequence of SEQ ID NO:1 or 2) or an agricultural composition comprising one or more SAMPs (e.g., HS peptides) described herein. In some embodiments, the SAMP or agricultural composition may be injected into the trunk of the plant. In other embodiments, the SAMP or agricultural composition may be injected into the stem of the plant. In yet other embodiments, the SAMP or agricultural composition may be foliar sprayed onto the plant. In yet other embodiments, the SAMP or agricultural composition may be applied by dripping irrigation to the plant. Once the plants are contacted with the SAMPs (e.g., HS peptides) described herein, the peptides may enhance HLB resistance or HLB tolerance of the plants, thus, preventing or treating HLB in the plants. 
     The methods described herein can be used to reduce symptoms caused by HLB, including yellowing of leaves, blotchy mottle of the leaves, zinc-deficiency-like mottle, severe chlorosis, and reduced fruit yield. It will be understood that symptoms of HLB vary according to the time of infection, stage of the disease, tree species, and tree maturity, among other things. It will be further understood that in some embodiments, the disclosed methods may not necessarily result in eradication or cure of the infection but can significantly reduce the symptoms caused by HLB. 
     Thus, in some embodiments, the methods provided herein reduce the symptoms of HLB by reducing the yellowing of leaves, resulting in a greener appearance, increasing the growth rate of the plant, and/or increasing the fruit yield of the plant. Thus, in some embodiments, the fruit yield is improved by 5%, 10%, 20%, 30%, 40%, 50%, 60% 70%, 80%, 90%, 100%, 200%, 500% or more compared to a plant that is not treated according to the methods. In some embodiments, the fruit yield is increased to 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% of the yield of a similar plant that was not infected by HLB. 
     The methods described herein may also be used to prevent HLB-infection in plants. For example, a plant that is not yet infected with HLB, but is at risk for infection (i.e., the plant is located in an area where HLB is identified in surrounding plants) may be contacted by one or more SAMPs (e.g., HS peptides) as described in the methods of the disclosure. The plant at risk for HLB may also be genetically modified to express one or more SAMPs (e.g., HS peptides) described herein to prevent HLB. 
     Potato ZC Disease 
     The present disclosure also provides methods of preventing or treating potato ZC disease in potato plants. In some embodiments of the methods, the plants with potato ZC disease may be contacted with a SAMP (e.g., an HS peptide) described herein (e.g., a SAMP comprising at least 75% sequence identity to the sequence of SEQ ID NOT or 2) or an agricultural composition comprising one or more SAMPs (e.g., HS peptides) described herein. In some embodiments, the SAMP or agricultural composition may be injected into the tuber of the plant. In other embodiments, the SAMP or agricultural composition may be applied to the roots of the plants. In yet other embodiments, the SAMP or agricultural composition may be foliar sprayed onto the plant. Once the plants are contacted with the SAMPs (e.g., HS peptides) described herein, the peptides may enhance potato ZC disease resistance or potato ZC disease tolerance of the plants, thus, preventing or treating potato ZC disease in the plants. 
     The methods described herein can be used to reduce symptoms caused by potato ZC disease, including chlorosis, leaf scorching, swollen nodes, vascular tissue browning, curled leaves, collapsed stolons, enlarged lenticels, vascular tissue browning, medullary ray discoloration, and necrotic flecking of tuber tissue. It will be understood that symptoms of potato ZC disease vary according to the time of infection, stage of the disease, plant species, and maturity, among other things. It will be further understood that in some embodiments, the disclosed methods may not necessarily result in eradication or cure of the infection, but can significantly reduce the symptoms caused by potato ZC disease. 
     Thus, in some embodiments, the methods provided herein reduce the symptoms of potato ZC disease as described above, resulting in a more healthy appearance, increasing the growth rate of the plant, and/or increasing the yield of the plant. Thus, in some embodiments, the yield is improved by 5%, 10%, 20%, 30%, 40%, 50%, 60% 70%, 80%, 90%, 100%, 200%, 500% or more compared to a plant that is not treated according to the methods. In some embodiments, the yield is increased to 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% of the yield of a similar plant that was not infected by potato ZC disease. 
     The methods described herein may also be used to prevent potato ZC disease-infection in plants. For example, a plant that is not yet infected with potato ZC disease, but is at risk for infection (i.e., the plant is located in an area where potato ZC disease is identified in surrounding plants) may be contacted by one or more SAMPs (e.g., HS peptides) as described in the methods of the disclosure. The plant at risk for potato ZC disease may also be genetically modified to express one or more SAMPs (e.g., HS peptides) described herein to prevent potato ZC disease. 
     V. Production of Plants Comprising SAMPs 
     In another aspect, the present disclosure provides for transgenic plants comprising recombinant expression cassettes for expressing a SAMP (e.g., an HS peptide) as described herein in a plant. In some embodiments, a transgenic plant is generated that contains a complete or partial sequence of a polynucleotide that is derived from a species other than the species of the transgenic plant. It should be recognized that transgenic plants encompass the plant or plant cell in which the expression cassette is introduced as well as progeny of such plants or plant cells that contain the expression cassette, including the progeny that have the expression cassette stably integrated in a chromosome. 
     A recombinant expression vector comprising a SAMP (e.g., an HS peptide) coding sequence driven by a heterologous promoter may be introduced into the genome of the desired plant host by a variety of conventional techniques. For example, the DNA construct may be introduced directly into the genomic DNA of the plant cell using techniques such as electroporation and microinjection of plant cell protoplasts, or the DNA construct can be introduced directly to plant tissue using ballistic methods, such as DNA particle bombardment. An exemplary vector is a viral vector that can express and optionally replicate in the plant. Exemplary viral vectors can include, for example,  citrus  tristeza vims (CTV) for expressing the peptide in a phloem-limited manner in  citrus , or tobacco rattle virus (TRV) to express the antimicrobial peptides in potato or other plants. Alternatively, the DNA construct may be combined with suitable T-DNA flanking regions and introduced into a conventional  Agrobacterium tumefaciens  host vector. The virulence functions of the  Agrobacterium tumefaciens  host will direct the insertion of the construct and adjacent marker into the plant cell DNA when the cell is infected by the bacteria. While transient expression of the constitutively active SAMP is encompassed by the disclosure, generally, expression of a construct of the disclosure will be from insertion of expression cassettes into the plant genome, e.g., such that at least some plant offspring also contain the integrated expression cassette. 
     Microinjection techniques are also useful for this purpose. These techniques are well known in the art and thoroughly described in the literature. The introduction of DNA constructs using polyethylene glycol precipitation is described in Paszkowski et al.  EMBO J.  3:2717-2722 (1984). Electroporation techniques are described in Fromm et al.  Proc. Natl. Acad Sci. USA  82:5824 (1985). Ballistic transformation techniques are described in Klein et al.  Nature  327:70-73 (1987). 
       Agrobacterium tumefaciens -mediated transformation techniques, including disarming and use of binary vectors, are well described in the scientific literature. See, for example, Horsch et al.  Science  233:496-498 (1984), and Fraley et al.  Proc. Natl. Acad. Sci. USA  80:4803 (1983). 
     Transformed plant cells derived by any of the above transformation techniques can be cultured to regenerate a whole plant that possesses the transformed genotype and thus the desired phenotype, e.g., resistance or tolerance to a  Liberibacter  disease (e.g., HLB). Such regeneration techniques rely on manipulation of certain phytohormones in a tissue culture growth medium, typically relying on a biocide and/or herbicide marker which has been introduced together with the desired nucleotide sequences. Plant regeneration from cultured protoplasts is described in Evans et al., Protoplasts Isolation and Culture, Handbook of Plant Cell Culture, pp. 124-176, MacMillilan Publishing Company, New York, 1983; and Binding, Regeneration of Plants, Plant Protoplasts, pp. 21-73, CRC Press, Boca Raton, 1985. Regeneration can also be obtained from plant callus, explants, organs, or parts thereof. Such regeneration techniques are described generally in Klee et al.  Ann. Rev. of Plant Phys.  38:467-486 (1987). 
     One of skill in the art will recognize that after the expression cassette is stably incorporated in transgenic plants and confirmed to be operable, it can be introduced into other plants by sexual crossing. Any of a number of standard breeding techniques can be used, depending upon the species to be crossed. 
     The expression cassettes and other constructs of the disclosure can be used to confer  Liberibacter  disease resistance or tolerance on essentially any plant. Thus, the disclosure has use over a broad range of plants, including species from the genus  Citrus  (e.g.,  Citrus maxima, Citrus medica, Citrus micrantha, Citrus reticulate, Citrus aurantiifolia, Citrus aurantium, Citrus latifolia, Citrus limon, Citrus limonia, Citrus paradise, Citrus sinensis , and  Citrus tangerine ) or species from the family Solanaceae (e.g.,  Solanum  spp.,  Capsicum  spp., and  Nicotiana  spp.). Species from the genus  Solanum  include, e.g.,  Solanum tuberosum, Solanum lycopersicum, Solanum melongena, Solanum aviculare, Solanum capsicastrum, Solanum crispum, Solanum laciniatum, Solanum laxum, Solanum pseudocapsicum, Solanum rantonnetii, Solanum seaforthianum , and  Solanum wendlandii . Species from the genus  Capsicum  include, e.g.,  Capsicum annuum, Capsicum baccatum, Capsicum campylopodium, Capsicum cardenasii, Capsicum chacoense, Capsicum cornutum, Capsicum dusenii, Capsicum eximium, Capsicum friburgense, Capsicum frutescens, Capsicum geminifolium, Capsicum havanense, Capsicum lanceolatum, Capsicum lycianthoides, Capsicum minutiflorum, Capsicum mositicum, Capsicum pubescens, Capsicum recurvatum, Capsicum schottianum, Capsicum spina - alba, Capsicum tovarii , and  Capsicum villosum . Species from the genus  Nicotiana  include, e.g.,  Nicotiana acuminate, Nicotiana benthamiana, Nicotiana glauca, Nicotiana longiflora, Nicotiana rustica, Nicotiana tabacum , and  Nicotiana occidentalis.    
     In particular embodiments, the plant is selected from the group consisting of  Citrus reticulata, Citrus sinensis, Citrus Clementina, Capsicum annuum, Solanum tuberosum, Solanum lycopersicum, Solanum melongena , and  Nitotiana benthamiana . In particular embodiments, the plant is a sweet orange plant ( Citrus sinensis ). In particular embodiments, the plant is a clementine plant ( Citrus clementina ). In particular embodiments, the plant is a potato plant ( Solanum tuberosum ). In some embodiment, the plant is a vegetable- or fruit-producing plant. 
     Those of skill will recognize that a number of plant species can be used as models to predict the phenotypic effects of transgene expression in other plants. For example, it is well recognized that both tobacco ( Nicotiana ) and  Arabidopsis  plants are useful models of transgene expression, particularly in other dicots. 
     In some embodiments, the plants of the disclosure have enhanced SAMP-mediated phenotypes, for example enhanced bacterial disease (e.g., a  Liberibacter  disease (e.g., HLB and ZC) and other bacterial diseases such as those caused by  Agrobacterium tumefaciens  (also known as  Rhizobium radiobacter ) and  Pseudomonas syringae ) resistance or tolerance, as compared to plants that are otherwise identical except for expression of the SAMP. 
     CRISPR/Cas 
     Plant gene manipulations can now be precisely tailored in non-transgenic organisms using the CRISPR/Cas9 genome editing method. In this bacterial antiviral and transcriptional regulatory system, a complex of two small RNAs—the CRISPR-RNA (crRNA) and the trans-activating crRNA (tracrRNA)—directs the nuclease (Cas9) to a specific DNA sequence complementary to the crRNA (Jinek, M., et al.  Science  337, 816-821 (2012)). Binding of these RNAs to Cas9 involves specific sequences and secondary structures in the RNA. The two RNA components can be simplified into a single element, the single guide-RNA (sgRNA), which is transcribed from a cassette containing a target sequence defined by the user (Jinek, M., et al.  Science  337, 816-821 (2012)). This system has been used for genome editing in humans, zebrafish,  Drosophila , mice, nematodes, bacteria, yeast, and plants (Hsu, P. D., et al.,  Cell  157, 1262-1278 (2014)). In this system the nuclease creates double stranded breaks at the target region programmed by the sgRNA. These can be repaired by non-homologous recombination, which often yields inactivating mutations. The breaks can also be repaired by homologous recombination, which enables the system to be used for gene targeted gene replacement (Li, J.-F., et al.  Nat. Biotechnol.  31, 688-691, 2013; Shan, Q., et al. Nat. Biotechnol. 31, 686-688, 2013). In some embodiments of the methods in the present disclosure, a gene encoding a wild-type or endogenous SAMP in a plant may be modified using the CAS9/CRISPR system to match the polynucleotide sequence encoding a SAMP described herein (e.g., a polynucleotide sequence encoding the SAMP having at least 75% sequence identity or at least one amino acid substitution relative to the sequence of any one of SEQ ID NOs:1-13 and 35-37 (e.g., SEQ ID NOs:1 and 2)). In some embodiments, a gene encoding a wild-type or endogenous SAMP in a plant may be modified using the CAS9/CRISPR system to match the polynucleotide sequence of any one of SEQ ID NOs: 14-26, 28-34, and 38-40 (e.g., SEQ ID NO: 14 and 15). 
     Accordingly, in some embodiments, instead of generating a transgenic plant, a native SAMP coding sequence in a plant or plant cell can be altered in situ to generate a plant or plant cell carrying a polynucleotide encoding a SAMP described herein (e.g., a SAMP having at least 75% sequence identity or at least one amino acid substitution relative to the sequence of any one of SEQ ID NOs: 1-13 and 35-37 (e.g., SEQ ID NOs:1 and 2)). For example, in some embodiments, CRISPR technology is used to introduce one or more nucleotide changes into a SAMP coding sequence in situ to change the appropriate codon to make a change corresponding to positions X 1  to X 25  as set forth in the sequence of SEQ ID NO:27. The CRISPR/Cas system has been modified for use in prokaryotic and eukaryotic systems for genome editing and transcriptional regulation. The “CRISPR/Cas” system refers to a widespread class of bacterial systems for defense against foreign nucleic acid. CRISPR/Cas systems are found in a wide range of eubacterial and archaeal organisms. CRISPR/Cas systems include type I, II, and III sub-types. Wild-type type II CRISPR/Cas systems utilize the RNA-mediated nuclease, Cas9 in complex with guide and activating RNA to recognize and cleave foreign nucleic acid. Cas9 homologs are found in a wide variety of eubacteria, including, but not limited to bacteria of the following taxonomic groups: Actinobacteria, Aquificae, Bacteroidetes-Chlorobi, Chlamydiae-Verrucomicrobia, Chlroflexi, Cyanobacteria, Firmicutes, Proteobacteria, Spirochaetes, and Thermotogae. An exemplary Cas9 protein is the  Streptococcus pyogenes  Cas9 protein. Additional Cas9 proteins and homologs thereof are described in, e.g., Chylinksi, et al., RNA Biol. 2013 May 1; 10(5): 726-737; Nat. Rev. Microbiol. 2011 June; 9(6): 467-477; Hou, et al., Proc Natl Acad Sci USA. 2013 Sep. 24; 110(39):15644-9; Sampson et al., Nature. 2013 May 9; 497(7448):254-7; and Jinek, et al., Science. 2012 Aug. 17; 337(6096):816-21. 
     Accordingly, in one aspect, a method is provided of using CRISPR/CAS9 to introduce at least one mutation into a plant cell is performed. In some embodiments, a method of altering a (e.g., native) nucleic acid encoding SAMP in a plant is provided. In some embodiments, the method comprises introducing into the plant cell containing and expressing a DNA molecule having a target nucleic acid encoding SAMP an engineered, non-naturally occurring Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-CRISPR associated (Cas) (CRISPR-Cas) system. In some embodiments, the CRISPR-Cas system comprises one or more vectors comprising: a) a first regulatory element operable in a plant cell operably linked to at least one nucleotide sequence encoding a CRISPR-Cas system guide RNA that hybridizes with the target sequence, and b) a second regulatory element operable in a plant cell operably linked to a nucleotide sequence encoding a Type-II Cas9 protein, wherein components (a) and (b) are located on same or different vectors of the system, whereby the guide RNA targets the target sequence and the Cas9 protein cleaves the DNA molecule, whereby at least one mutation is introduced into the target nucleic acid encoding the SAMP, i.e., one or more mutations are introduced into the target nucleic acid encoding the SAMPs to alter the sequence of the target nucleic acid to match the polynucleotide sequence encoding an antimicrobial (e.g., antibacterial) peptide having the sequence of any one of SEQ ID NOs:1-13 and 35-37 (e.g., SEQ ID NOs:1 and 2). In some embodiments, the SAMP is selected from any of SEQ ID NOs:1-5 and 9, or a substantially identical polypeptide thereof. 
     In some embodiments, methods of using CRISPR/CAS9 technology to introduce at least one mutation into a (e.g., native) nucleic acid encoding SAMP may be applied to a broad range of plants, including species from the genus  Citrus  (e.g.,  Citrus maxima, Citrus medica, Citrus micrantha, Citrus reticulate, Citrus aurantiifolia, Citrus aurantium, Citrus latifolia, Citrus limon, Citrus limonia, Citrus paradise, Citrus sinensis , and  Citrus tangerine ) or species from the family Solanaceae (e.g.,  Solanum  spp.,  Capsicum  spp., and  Nicotiana  spp.). Species from the genus  Solanum  include, e.g.,  Solanum tuberosum, Solanum lycopersicum, Solanum melongena, Solanum aviculare, Solanum capsicastrum, Solanum crispum, Solanum laciniatum, Solanum laxum, Solanum pseudocapsicum, Solanum rantonnetii, Solanum seaforthianum , and  Solanum wendlandii . Species from the genus  Capsicum  include, e.g.,  Capsicum annuum, Capsicum baccatum, Capsicum campylopodium, Capsicum cardenasii, Capsicum chacoense, Capsicum cornutum, Capsicum dusenii, Capsicum eximium, Capsicum friburgense, Capsicum frutescens, Capsicum geminifolium, Capsicum havanense, Capsicum lanceolatum, Capsicum lycianthoides, Capsicum minutiflorum, Capsicum mositicum, Capsicum pubescens, Capsicum recurvatum, Capsicum schottianum, Capsicum spina - alba, Capsicum tovarii , and  Capsicum villosum . Species from the genus  Nicotiana  include, e.g.,  Nicotiana acuminate, Nicotiana benthamiana, Nicotiana glauca, Nicotiana longiflora, Nicotiana rustica, Nicotiana tabacum , and  Nicotiana occidentalis . In particular embodiments, the plant is selected from the group consisting of  Citrus reticulata, Citrus sinensis, Citrus Clementina, Capsicum annuum, Solanum tuberosum, Solanum lycopersicum, Solanum melongena , and  Nitotiana benthamiana . In particular embodiments, the plant is a sweet orange plant ( Citrus sinensis ). In particular embodiments, the plant is a clementine plant ( Citrus  Clementina). In particular embodiments, the plant is a potato plant ( Solanum tuberosum ). In some embodiment, the plant is a vegetable- or fruit-producing plant. 
     In some embodiments, the mutation(s) introduced to the target nucleic acid sequence change the appropriate codon in the sequence to make change(s) corresponding to positions X 1  to X 25  as set forth in the sequence of SEQ ID NO:27. For example, after introducing the mutations to the target nucleic acid to change the appropriate codons, the modified nucleic acid sequence encode, at its corresponding positions, one or more amino acids as set forth in positions X 1  to X 25  of SEQ ID NO:27. Also provided as a plant or plant cell resulting from the above-described method. Such a plant will contain a non-naturally-occurring nucleic acid sequence encoding the SAMP. 
     VI. Expression Cassettes 
     In some embodiments, the present disclosure provides expression cassettes comprising a polynucleotide encoding a SAMP (e.g., an HS peptide) of the disclosure, wherein introduction of the expression cassette into a plant results in a transgenic plant expressing the SAMP. In some embodiments, a promoter may be operably linked to the polynucleotide encoding the SAMP. The promoter may be heterologous to the polynucleotide. In some embodiments, the promoter may be inducible. In some embodiments, the promoter may plant tissue-specific (e.g., phloem-specific, tuber-specific, root-specific, stem-specific, trunk-specific, or leaf-specific). 
     Any of a number of means well known in the art can be used to drive SAMP expression in plants. Any organ can be targeted, such as shoot vegetative organs/structures (e.g. leaves, stems, and tubers), roots, flowers and floral organs/structures (e.g. bracts, sepals, petals, stamens, carpels, anthers and ovules), seed (including embryo, endosperm, and seed coat) and fruit. Alternatively, the polynucleotide encoding a SAMP (e.g., an HS peptide) described herein can be expressed specifically in certain cell and/or tissue types within one or more organs (e.g., guard cells in leaves using a guard cell-specific promoter). Alternatively, the polynucleotide encoding a SAMP (e.g., an HS peptide) described herein can be expressed constitutively (e.g., using the CaMV 35S promoter). 
     To use a polynucleotide encoding a SAMP (e.g., an HS peptide) described herein in the above techniques, recombinant DNA vectors suitable for transformation of plant cells are prepared. Techniques for transforming a wide variety of higher plant species are well known and described in the technical and scientific literature. See, e.g., Weising et al  Ann. Rev. Genet.  22:421-477 (1988). A DNA sequence coding for the SAMP preferably will be combined with transcriptional and translational initiation regulatory sequences which will direct the transcription of the sequence from the gene in the intended tissues of the transformed plant. 
     For example, a plant promoter fragment may be employed to direct expression of the SAMP (e.g., an HS peptide) in all tissues of a transgenic plant. Such promoters are referred to herein as “constitutive” promoters and are active under most environmental conditions and states of development or cell differentiation. Examples of constitutive promoters include the cauliflower mosaic virus (CaMV) 35S transcription initiation region, the 1′- or 2′-promoter derived from T-DNA of  Agrobacterium tumafaciens , and other transcription initiation regions from various plant genes known to those of skill. 
     Alternatively, the plant promoter may direct expression of the SAMP (e.g., an HS peptide) in a specific tissue (tissue-specific promoters) or may be otherwise under more precise environmental control (inducible promoters). Examples of tissue-specific promoters under developmental control include promoters that initiate transcription only in certain tissues, such as phloem, tubers, stems, trunks, leaves, or guard cells. Examples of environmental conditions that may affect transcription by inducible promoters include, but are not limited to, anaerobic conditions, elevated temperature, and the presence of light. 
     In some embodiments, a polyadenylation region at the 3′-end of the coding region of the SAMP may be included. The polyadenylation region can be derived from a naturally occurring SAMP gene, from a variety of other plant genes, or from T-DNA. 
     The vector comprising the polynucleotide sequences (e.g., promoters or SAMP coding regions) may include a marker gene that confers a selectable phenotype on plant cells. For example, the marker may encode biocide resistance, particularly antibiotic resistance, such as resistance to kanamycin, G418, bleomycin, hygromycin, or herbicide resistance, such as resistance to chlorosluforon or Basta. 
     In some embodiments, the polynucleotide encoding the SAMP (e.g., an HS peptide) is expressed recombinantly in plant cells. A variety of different expression constructs, such as expression cassettes and vectors suitable for transformation of plant cells, can be prepared. Techniques for transforming a wide variety of higher plant species are well known and described in the technical and scientific literature. See, e.g., Weising et al.  Ann. Rev. Genet.  22:421-477 (1988). A DNA sequence coding for a SAMP (e.g., an HS peptide) described herein can be combined with cA-acting (promoter) and trans-acting (enhancer) transcriptional regulatory sequences to direct the timing, tissue type, and levels of transcription in the intended tissues of the transformed plant. Translational control elements can also be used. 
     Embodiments of the present disclosure also provide for a polynucleotide encoding the SAMP (e.g., an HS peptide) to be operably linked to a promoter which, in some embodiments, is capable of driving the transcription of the SAMP coding sequence in plants. The promoter can be, e.g., derived from plant or viral sources. The promoter can be, e.g., constitutively active, inducible, or tissue specific. In construction of recombinant expression cassettes, vectors, transgenics, of the disclosure, a different promoter can be chosen and employed to differentially direct gene expression, e.g., in some or all tissues of a plant or animal. 
     Constitutive Promoters 
     A fragment can be employed to direct expression of a polynucleotide encoding the SAMP (e.g., an HS peptide) in all transformed cells or tissues, e.g., as those of a transgenic plant. The term “constitutive regulatory element” means a regulatory element that confers a level of expression upon an operatively linked nucleic molecule that is relatively independent of the cell or tissue type in which the constitutive regulatory element is expressed. A constitutive regulatory element that is expressed in a plant generally is widely expressed in a large number of cell and tissue types. Promoters that drive expression continuously under physiological conditions are referred to as “constitutive” promoters and are active under most environmental conditions and states of development or cell differentiation. 
     A variety of constitutive regulatory elements useful for ectopic expression in a transgenic plant are well known in the art. The cauliflower mosaic virus 35S (CaMV 35S) promoter, for example, is a well-characterized constitutive regulatory element that produces a high level of expression in all plant tissues (Odell et al.,  Nature  313:810-812 (1985)). The CaMV 35S promoter can be particularly useful due to its activity in numerous diverse plant species (Benfey and Chua,  Science  250:959-966 (1990); Futterer et al.,  Physiol. Plant  79:154 (1990); Odell et al., supra, 1985). A tandem 35S promoter, in which the intrinsic promoter element has been duplicated, confers higher expression levels in comparison to the unmodified 35S promoter (Kay et al.,  Science  236:1299 (1987)). Other useful constitutive regulatory elements include, for example, the cauliflower mosaic vims 19S promoter; the Figwort mosaic virus promoter; and the nopaline synthase (nos) gene promoter (Singer et al.,  Plant Mol. Biol.  14:433 (1990); An,  Plant Physiol.  81:86 (1986)). 
     Additional constitutive regulatory elements including those for efficient expression in monocots also are known in the art, for example, the pEmu promoter and promoters based on the rice Actin-1 5′ region (Last et al,  Theor. Appl. Genet.  81:581 (1991); Mcelroy et al.,  Mol. Gem Genet.  231:150 (1991); Mcelroy et al.,  Plant Cell  2:163 (1990)). Chimeric regulatory elements, which combine elements from different genes, also can be useful for ectopically expressing a nucleic acid molecule encoding a SAMP (e.g., an HS peptide) described herein (Comai et al.,  Plant Mol. Biol.  15:373 (1990)). 
     Other examples of constitutive promoters include the 1′- or 2′-promoter derived from T-DNA of  Agrobacterium  tumafaciens (see, e.g., Mengiste (1997) supra; O&#39;Grady (1995)  Plant Mol. Biol.  29:99-108); actin promoters, such as the  Arabidopsis  actin gene promoter (see, e.g., Huang (1997)  Plant Mol. Biol.  1997 33:125-139); alcohol dehydrogenase (Adh) gene promoters (see, e.g., Millar (1996)  Plant Mol. Biol.  31:897-904); ACTII from  Arabidopsis  (Huang et al.  Plant Mol. Biol.  33:125-139 (1996)), Cat3 from  Arabidopsis  (GenBank No. U43147, Zhong et al,  Mol. Gen. Genet.  251:196-203 (1996)), the gene encoding stearoyl-acyl carrier protein desaturase from  Brassica napus  (Genbank No. X74782, Solocombe et al.  Plant Physiol.  104:1167-1176 (1994)), GPc1 from maize (GenBank No. X15596, Martinez et al  J. Mol. Biol  208:551-565 (1989)), Gpc2 from maize (GenBank No. U45855, Manjunath et al,  Plant Mol. Biol.  33:97-112 (1997)), other transcription initiation regions from various plant genes known to those of skill. See also Holtorf  Plant Mol Biol.  29:637-646 (1995). 
     Inducible Promoters 
     Alternatively, a plant promoter may direct expression of the polynucleotide encoding the SAMP (e.g., an HS peptide) under the influence of changing environmental conditions or developmental conditions. Examples of environmental conditions that may affect transcription by inducible promoters include anaerobic conditions, elevated temperature, drought, or the presence of light. Such promoters are referred to herein as “inducible” promoters. In some embodiments, an inducible promoter is one that is induced by one or more environmental stressors, including but not limited to, drought, freezing cold, and high salt. For example, the disclosure can incorporate a drought-specific promoter such as a drought-inducible promoter of maize (e.g., the maize rab17 drought-inducible promoter (Vilardell et al. (1991)  Plant Mol. Biol  17:985-993; Vilardell et al. (1994)  Plant Mol. Biol  24:561-569)); or alternatively a cold, drought, and high salt inducible promoter from potato (Kirch (1997)  Plant Mol. Biol.  33:897-909) or from  Arabidopsis  (e.g., the rd29A promoter (Kasuga et al. (1999)  Nature Biotechnology  17:287-291). Other environmental stress-inducible promoters include promoters from the following genes: Rab21, Wsi18, Lea3, Uge1, Dip1, and R1G1B in rice (Yi et al (2010)  Planta  232:743-754). 
     In some embodiments, a plant promoter is a stress-inducible promoter (e.g., a drought-, cold-, or salt-inducible promoter) that comprises a dehydration-responsive element (DRE) and/or an ABA-responsive element (ABRE), including but not limited to the rd29A promoter. 
     Alternatively, plant promoters which are inducible upon exposure to plant hormones, such as auxins, are used to express the polynucleotide encoding the SAMP (e.g., an HS peptide). For example, the disclosure can use the auxin-response elements E1 promoter fragment (AuxREs) in the soybean ( Glycine max  L.) (Liu (1997)  Plant Physiol.  115:397-407); the auxin-responsive  Arabidopsis  GST6 promoter (also responsive to salicylic acid and hydrogen peroxide) (Chen (1996) Plant J. 10: 955-966); the auxin-inducible parC promoter from tobacco (Sakai (1996) 37:906-913); a plant biotin response element (Streit (1997)  Mol. Plant Microbe Interact.  10:933-937); and, the promoter responsive to the stress hormone abscisic acid (Sheen (1996) Science 274:1900-1902). 
     Plant promoters inducible upon exposure to chemicals reagents that may be applied to the plant, such as herbicides or antibiotics, are also useful for expressing the polynucleotide encoding the SAMP (e.g., an HS peptide). For example, the maize In2-2 promoter, activated by benzenesulfonamide herbicide safeners, can be used (De Veylder (1997)  Plant Cell Physiol.  38:568-577); application of different herbicide safeners induces distinct gene expression patterns, including expression in the root, hydathodes, and the shoot apical meristem. A SAMP (e.g., an HS peptide) coding sequence can also be under the control of, e.g., a tetracycline-inducible promoter, e.g., as described with transgenic tobacco plants containing the  Avena sativa  L. (oat) arginine decarboxylase gene (Masgrau (1997)  Plant J.  11:465-473); or, a salicylic acid-responsive element (Stange (1997)  Plant J.  11:1315-1324; Uknes et al.,  Plant Cell  5:159-169 (1993); Bi et al.,  Plant J.  8:235-245 (1995)). 
     Examples of useful inducible regulatory elements include copper-inducible regulatory elements (Mett et al.,  Proc. Natl. Acad. Sci. USA  90:4567-4571 (1993); Furst et al.,  Cell  55:705-717 (1988)); tetracycline and chlor-tetracycline-inducible regulatory elements (Gatz et al, Plant J. 2:397-404 (1992); Röder et al.,  Mol. Gem Genet.  243:32-38 (1994); Gatz,  Meth. Cell Biol.  50:411-424 (1995)); ecdysone inducible regulatory elements (Christopherson et al.,  Proc. Natl. Acad Sci. USA  89:6314-6318 (1992); Kreutzweiser et al., Ecotoxicol. Environ. Safety 28:14-24 (1994)); heat shock inducible regulatory elements (Takahashi et al.,  Plant Physiol.  99:383-390 (1992); Yabe et al.,  Plant Cell Physiol.  35:1207-1219 (1994); Ueda et al.,  Mol. Gem Genet.  250:533-539 (1996)); and lac operon elements, which are used in combination with a constitutively expressed lac repressor to confer, for example, IPTG-inducible expression (Wilde et al,  EMBO J.  11:1251-1259 (1992)). An inducible regulatory element useful in the transgenic plants of the disclosure also can be, for example, a nitrate-inducible promoter derived from the spinach nitrite reductase gene (Back et al.,  Plant Mol. Biol.  17:9 (1991)) or a light-inducible promoter, such as that associated with the small subunit of RuBP carboxylase or the LHCP gene families (Feinbaum et al.,  Mol. Gem Genet.  226:449 (1991); Lam and Chua,  Science  248:471 (1990)). 
     Tissue-Specific Promoters 
     Alternatively, the plant promoter may direct expression of the polynucleotide encoding the SAMP (e.g., an HS peptide) in a specific tissue (tissue-specific promoters). Tissue specific promoters are transcriptional control elements that are only active in particular cells or tissues at specific times during plant development, such as in vegetative tissues or reproductive tissues. 
     Examples of tissue-specific promoters under developmental control include promoters that initiate transcription only (or primarily only) in certain tissues, such as vegetative tissues, e.g., roots or leaves, or reproductive tissues, such as fruit, ovules, seeds, pollen, pistols, flowers, or any embryonic tissue, or epidermis or mesophyll. Reproductive tissue-specific promoters may be, e.g., ovule-specific, embryo-specific, endosperm-specific, integument-specific, seed and seed coat-specific, pollen-specific, petal-specific, sepal-specific, or some combination thereof. In some embodiments, the promoter is cell-type specific, e.g., guard cell-specific. 
     Epidermal-specific promoters include, for example, the  Arabidopsis  LTPI promoter (Thoma et al. (1994)  Plant Physiol.  105(1):35-45), the CER1 promoter (Aarts et al. (1995)  Plant Cell  7:2115-27), and the CER6 promoter (Hooker et al. (2002)  Plant Physiol  129:1568-80), and the orthologous tomato LeCER6 (Vogg el al. (2004)  J. Exp Bot.  55:1401-10). 
     Guard cell-specific promoters include, for example, the DGP1 promoter (Li et al. (2005)  Science China C Life Sci.  48:181-186). 
     Other tissue-specific promoters include seed promoters. Suitable seed-specific promoters are derived from the following genes: MAC1 from maize (Sheridan (1996)  Genetics  142:1009-1020); Cat3 from maize (GenBank No. L05934, Abler (1993)  Plant Mol Biol.  22:10131-1038); vivparous-1 from  Arabidopsis  (Genbank No. U93215); atmyc1 from  Arabidopsis  (Urao (1996)  Plant Mol. Biol  32:571-57; Conceicao (1994) Plant 5:493-505); napA from  Brassica napus  (GenBank No. J02798, Josefsson (1987) JBL 26:12196-1301); and the napin gene family from  Brassica napus  (Sjodahl (1995)  Planta  197:264-271). 
     A variety of promoters specifically active in vegetative tissues, such as leaves, stems, roots and tubers, can also be used to express polynucleotide encoding SAMPs (e.g., HS peptides) described herein. For example, promoters controlling patatin, the major storage protein of the potato tuber, can be used, see, e.g., Kim (1994)  Plant Mol. Biol.  26:603-615; Martin (1997)  Plant J.  11:53-62. The ORF13 promoter from  Agrobacterium rhizogenes  that exhibits high activity in roots can also be used (Hansen (1997)  Mol. Gen. Genet.  254:337-343. Other useful vegetative tissue-specific promoters include: the tarin promoter of the gene encoding a globulin from a major taro ( Colocasia esculenta  L. Schott) corm protein family, tarin (Bezerra (1995)  Plant Mol. Biol.  28:137-144); the curculin promoter active during taro corm development (de Castro (1992)  Plant Cell  4:1549-1559) and the promoter for the tobacco root-specific gene TobRB7, whose expression is localized to root meristem and immature central cylinder regions (Yamamoto (1991)  Plant Cell  3:371-382). 
     Leaf-specific promoters, such as the ribulose biphosphate carboxylase (RBCS) promoters, can also be used. For example, the tomato RBCS1, RBCS2 and RBCS3A genes are expressed in leaves and light-grown seedlings, only RBCS1 and RBCS2 are expressed in developing tomato fruits (Meier (1997)  FEBS Lett.  415:91-95). Ribulose bisphosphate carboxylase promoters expressed almost exclusively in mesophyll cells in leaf blades and leaf sheaths at high levels, described by Matsuoka (1994) Plant J. 6:311-319, can be used. Another leaf-specific promoter is the light harvesting chlorophyll a/b binding protein gene promoter, see, e.g., Shiina (1997)  Plant Physiol.  115:477-483; Casal (1998)  Plant Physiol.  116:1533-1538. The  Arabidopsis thaliana  myb-related gene promoter (Atmyb5) described by Li (1996)  FEBS Lett.  379:117-121, is leaf-specific. The Atmyb5 promoter is expressed in developing leaf trichomes, stipules, and epidermal cells on the margins of young rosette and cauline leaves, and in immature seeds. Atmyb5 mRNA appears between fertilization and the 16-cell stage of embryo development and persists beyond the heart stage. A leaf promoter identified in maize by Busk (1997)  Plant J.  11:1285-1295, can also be used. 
     Another class of useful vegetative tissue-specific promoters are meristematic (root tip and shoot apex) promoters. For example, the “SHOOTMERISTEMLESS” and “SCARECROW” promoters, which are active in the developing shoot or root apical meristems, described by Di Laurenzio (1996)  Cell  86:423-433; and, Long (1996)  Nature  379:66-69; can be used. Another useful promoter is that which controls the expression of 3-hydroxy-3-methylglutaryl coenzyme A reductase HMG2 gene, whose expression is restricted to meristematic and floral (secretory zone of the stigma, mature pollen grains, gynoecium vascular tissue, and fertilized ovules) tissues (see, e.g., Enjuto (1995)  Plant Cell.  7:517-527). Also useful are kn1-related genes from maize and other species which show meristem-specific expression, see, e.g., Granger (1996)  Plant Mol. Biol.  31:373-378; Kerstetter (1994)  Plant Cell  6:1877-1887; Hake (1995)  Philos. Trans. R. Soc. Lond. B. Biol. Sci.  350:45-51. For example, the  Arabidopsis thaliana  KNAT1 promoter (see, e.g., Lincoln (1994)  Plant Cell  6:1859-1876). 
     One of skill will recognize that a tissue-specific promoter may drive expression of operably linked sequences in tissues other than the target tissue. Thus, as used herein a tissue-specific promoter is one that drives expression preferentially in the target tissue, but may also lead to some expression in other tissues as well. 
     In another embodiment, the polynucleotide encoding the SAMP (e.g., an HS peptide) is expressed through a transposable element. This allows for constitutive, yet periodic and infrequent expression of the constitutively active polypeptide. The disclosure also provides for use of tissue-specific promoters derived from viruses including, e.g., the tobamovirus subgenomic promoter (Kumagai (1995)  Proc. Natl. Acad. Sci. USA  92:1679-1683; the rice tungro bacilliform virus (RTBV), which replicates only in phloem cells in infected rice plants, with its promoter which drives strong phloem-specific reporter gene expression; the cassava vein mosaic vims (CVMV) promoter, with highest activity in vascular elements, in leaf mesophyll cells, and in root tips (Verdaguer (1996)  Plant Mol. Biol.  31:1129-1139). 
     In another embodiment, the present disclosure provides for expression vectors comprising an expression cassette of the disclosure (e.g., as described herein). 
     VII. Plants 
     In some embodiments, the plant is a  citrus  plant. In some embodiments, the  citrus  plant is an orange tree, a lemon tree, a lime tree, or a grapefruit tree. In one embodiment, the  citrus  plant is a navel orange, Valencia orange, sweet orange, mandarin orange, or sour orange. In one embodiment, the  citrus  plant is a lemon tree. In one embodiment, the  citrus  plant is a lime tree. In some embodiments, the plant is a relative of a  citrus  plant, such as orange jasmine, limeberry, and trifoliate orange. In some embodiments, the plant is a potato plant. 
     In some embodiments, the present disclosure provides for plants (or a plant cell, seed, flower, leaf, fruit, or other plant part from such plants or processed food or food ingredient from such plants) comprising an expression cassette comprising a promoter operably linked to a polynucleotide encoding a SAMP (e.g., an HS peptide) of the disclosure (e.g., as described herein). In some embodiments, the plant has decreased UBC expression or activity and/or increased expression or activity of Pi transporters. 
     EXAMPLES 
     Example 1—Expression of Antimicrobial SAMP Genes 
     The expression levels of SAMPs in HLB-susceptible and HLB-tolerant plants were detected by quantitative RT-PCR. The expression level of  citrus  actin was used as an internal control. The expression level of SAMPs is higher in two different HLB-tolerant/resistant varieties from totally different geographic and genetic backgrounds (a hybrid of Cleopatra mandarin ( Citrus reticulata ) and  Poncirus trifoliate  US942, and a  Eremocitrus glauca  hybrid) than in their corresponding HLB-sensitive close relatives ( FIGS. 1A and 1B ). 
     Example 2—Effects of SAMPs in Suppressing  Candidatus Liberibacter Solanacearum  ( Ca. L. Solanacearum ) Infection 
     Solanaceae plant  Nicotiana benthamiana  ( Nb ) is commonly used for gene function studies against pathogen infections.  Nb  can be infected by  Ca. L. solanacearum  by being infested with  Ca. L. solanacearum -positive potato psyllid, which is a pathosystem highly similar to potato ZC disease and  citrus  HLB. The effects of two SAMPs, CghSAMPa and CghSAMPb (SEQ ID NOs:1 and 2, respectively, which are hybrids from crossing  Citrus glauca  with  Citrus  sp.), were tested using the  Nb /potato psyllid/Ca. L  solanacearum  pathosystem. The CghSAMPa and CghSAMPb peptides were expressed and purified in  E. coli . Ca. L  solanacearum -infected  Nb  plants were treated with 30 μM CghSAMPa or CghSAMPb peptide, or mock solution by stem injection. The photos in  FIG. 3A  were taken after 3 weeks of treatment.  FIG. 3A  shows that the infected plants treated with the SAMPs were able to grow much better than the plants that received mock treatment.  FIGS. 3B and 7  further show that the plants treated with CghSAMPa and CghSAMPb peptides had much lower bacterial titer compared to the plants treated with mock solution. The results demonstrated that the two SAMPs from resistant/tolerant  citrus  rootstocks significantly controlled the titer of  Ca. L. solanacearum  in  Nb  plants and promoted plant growth. 
     Example 3—Effects of SAMPs Delivered Via Trunk Delivery 
     We have tested effective SAMP treatment on HLB-positive  citrus  plants using trunk delivery method, and the bacterial titer of all the treated trees are largely reduced, about 30-100 folds. No bacteria were detected in the treated trees. All the new shoots and leaves from the treated trees were no longer symptomatic, and the new shoots and leaves from the mock treated plants still have yellow patch symptoms ( FIG. 4 ) 
     Example 4—Effects of SAMPs in Suppressing  Candidatus Liberibacter Solanacearum  ( Ca. L. Solanacearum ) Infection in Potato and Tomato 
     We have also performed the effective SAMP treatment on C. Lso-infected potato. The disease symptom was clearly inhibited, and the yield of tuber production was increased. ( FIG. 5 ) 
     We also tested the effective SAMP on C. Lso-infected tomato, and the disease symptom was largely reduced as well. ( FIG. 6 ) 
     Example 5—Effects of SAMPs in  Citrus  Plants 
     SAMP was apply by foliar sprayed with 5% Southern Ag Methylated Seed Oil (MSO) on the 1 year old seedlings. The expression level of defense response marker genes CsPR1, CsPR2, and CAPAL were evaluated by qRT-PCR with the ubiquitin gene as an internal control for up to 7 days after treatment.  FIGS. 8A-8C  show that SAMPs primed the  citrus  plants to have increased expression of the defense response marker genes. 
     Further, different concentrations of SAMP solutions were infiltrated into sweet orange leaves. No cell death was observed with 30 μM treatment.  FIGS. 9A and 9B  show that SAMPs have low phytotoxic activity on  citrus  leaves. 
     Moreover, mRNA expression analysis ( FIG. 10 ) demonstrates that SAMPs are highly expressed in the fruit of Australian finger lime, Australian desert lime, lemon, and  Poncirus trifoliate  (common root stock), which have already been consumed by humans for hundreds of years. The mRNA expression was detected by RT-PCR. 
     Example 6—Protease Digestion of SAMPs 
       FIG. 11  shows that SAMPs are sensitive to human protease pepsin, a major gastric enzyme. 20 μg of SAMP were incubated with 0.4% solution of pepsin in 10 mM HCl at 37° C. The reaction was analyzed with 18% SDS-PAGE gel and visualized with coomassie blue staining. SAMP was completely digested within 45 min. 
     Example 7—Stability of SAMPs 
     SAMPs were incubated at room temperature (RT) for 24 hours, 60° C. for 24 hours, or 100° C. for 20 mins. Subsequently, the SAMPs were used for viability/cytotoxicity assay. The assay was done by incubating 10 7  cells/mL of  Liberbacter crescens  with the pre-treated SAMP or buffer only as mock treatment for 2 hours. The samples were then stained with DMAO (green) and EthD-III (orange), which represent live and dead cells, respectively.  FIG. 12  shows that SAMPs are stable at up to 100° C. 
     Further, to investigate the stability of SAMPs in  citrus  plants, 20 μg of SAMPs were incubated with 200 μg fresh  citrus  lysate in 1×PBS buffer at room temperature. The reaction was analyzed with 18% SDS-PAGE gel and visualized with coomassie blue staining.  FIG. 13  shows that SAMPs are stable in  citrus  cell lysate, which indicates that they are also stable in trees. 
     Example 8—Additional Antimicrobial Activity of SAMPs 
     The antimicrobial activity of SAMPs against other Gram-negative bacterial pathogens was tested. Specifically, activity against  Pseudomonas syringae  and  Agrobacterium tumefaciens  was verified by agar diffusion assay,  FIG. 14A  and  FIG. 14B  respectively. Each essay was done by applying 10 μL SAMPs on the medium with bacteria, where the concentration for SAMPs was 100 μM for  Pseudomonas syringae  and 150 μM for  Agrobacterium tumefaciens  respectively. The culture plates were incubated at 28° C. and observed after 24 hours. The rings without bacterial growth confirm antimicrobial activity. 
     In addition, SAMPs were incubated at 4° C. for 24 hours, RT for 24 hours, or 60° C. for 24 hours. Subsequently, the SAMPs were used for viability/cytotoxicity assay. The assay was done by incubating 10 7  cells/mL of  Agrobacterium tumefaciens  with the pre-treated SAMP or buffer only as mock treatment for 2 hours. The samples were then stained with DMAO (green) and EthD-III (orange), which represent live and dead cells, respectively. FIG.  15  shows that SAMPs are stable and have antimicrobial activity against  Agrobacterium tumefaciens  up to 60° C. 
     One or more features from any embodiments described herein or in the figures may be combined with one or more features of any other embodiment described herein in the figures without departing from the scope of the disclosure. 
     All publications, patents and patent applications cited in this specification are herein incorporated by reference as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Although the foregoing disclosure has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be readily apparent to those of ordinary skill in the art in light of the teachings of this disclosure that certain changes and modifications may be made thereto without departing from the spirit or scope of the appended claims.