# Patent

## Title
Commercial production of recombinant manganese-dependent peroxidase in plants

## Abstract

Expression of a recombinant manganese-dependent peroxidase in plants is described. Methods for the recovery of transgenic corn seeds that express high levels of functional manganese-dependent peroxidase are also provided. Manganese-dependent peroxidase vectors are engineered to contain sequences directing seed-preferred expression as well as sequences for cell wall-targeted localization.

## Background
This application claims priority to U.S. Ser. No. 60/387,700, filed Jun. 11, 2002, which is incorporated by reference in its entirety.


FIELD OF THE INVENTION
The present invention relates to commercial production of heterologous proteins in plants. More specifically, the invention is to novel methods of overexpressing a heterologous, fungally-derived, manganese-dependent peroxidase in corn plants and to methods of targeting expression of manganese-dependent peroxidase to the cell wall of corn seeds. The present invention also relates to methods for the efficient recovery of fully active manganese-dependent peroxidase enzyme from corn seeds and to use of such proteins in commercial applications.
BACKGROUND OF THE INVENTION
Manganese-dependent peroxidases (or manganese peroxidases) are ligninolytic enzymes produced by white rot fungi. One such fungus is the basidiomycete Phanerochaete chrysosporium which is capable of degrading lignin to the point of mineralization with H2O and CO2 as the final products. This degrading ability is due to the exocellular peroxidases such as various isozymes of lignin peroxidases (LiP) and manganese peroxidases (MnP) along with an extracellular H2O2-generating system. Manganese peroxidases are glycosylated heme protein peroxidases that catalyze the H2O2-dependent oxidation of Mn2+ to Mn3+. Mn3+ is subsequently chelated by organic acids to create the diffusible oxidants that attack phenolic lignin structures (Kishi et al. 1994. Mechanism of manganese peroxidase compound II reduction. Effect of organic chelators and pH. Biochemistry 33: 8694–8701).
Several isozymes of manganese peroxidases from the fungus Phanerochaete chrysosporium have been described (Tien and Kirk. 1983. Lignin-degrading enzyme from the hymenomycete Phanerochaete chrysosporium Burds. Science 221: 661–663; Glenn et al. 1983. An extracellular H2O2-requiring enzyme preparation involved in lignin biodegradation by the white rot basidiomycete Phanerochaete chrysosporium. Biochem. Biophys. Res. Commun. 114: 1077–1083; Kuwahara et al. 1984. Separation and characterization of two extracellular H2O2-dependent oxidases from ligninolytic cultures of Phanerochaete chrysosporium. FEBS Lett. 169: 247–250) and the major isozyme, MnPI (H3) has been characterized in detail (Gold and Alic. 1993. Molecular biology of the lignin-degrading basidiomycete Phanerochaete chrysosporium. Microbiol. Rev. 57:605–622) and its X-ray structure reported (Sundaramoorthy, M., K. Kishi, M. H. Gold, and T. L. Poulos. 1994. The crystal structure of manganese peroxidase from Phanerochaete chrysosporium at 2.06-A resolution. J Biol. Chem. 269:32759–32767). These isozymes are encoded by a family of structurally related genes that are expressed under nutrient-limiting conditions during secondary metabolic growth phase of the fungus (Gettemy et al. 1998. Reverse transcription-PCR analysis of the regulation of the manganese peroxidase gene family. Appl Environ Microbiol 64(2): 569–74).
Commercial production of MnP enzymes has its application in the fields of paper making, waste treatment, bioremediation and others. In the pulp and paper industry, biological pulping and biological bleaching have the potential of improving the quality of pulp and paper, reducing energy costs and environmental pollution relative to traditional pulping and bleaching operations (U.S. Pat. No. 5,691,193). The technology has focused on white rot fungi that have complex extracellular ligninolytic enzymes such as MnP and LiP. Unlike the xylanases used in commercial bleaching to degrade hemicelluloses, peroxidases such as LiP and MnP have not been much tested in applications for manufacturing processes. This is simply due to the fact that effective methods for the production of commercially viable yields of enzyme have not been developed. Scale-up to industrial process requirements presents challenges that are difficult to simulate in the laboratory or pilot-scale tests. Thus there is a need in industry for large-scale production of ligninolytic enzymes such as MnP.
Large-scale production of MnP may also be employed in the treatment of environmental pollutants such as the cleanup of textile mill effluents as well as the bioremediation of dye-contaminated soil. For example, textile effluents cause a high environmental impact when released into the environment without correct treatment. Azo dyes are important synthetic compounds that are widely used in the dyestuff and textile industries. They are not biodegradable and tend to persist in the environment unless subjected to costly physical-chemical decontamination processes. Disperse Yellow 3 [2-(4′-acetamidophenylazo)-4-methylphenol] (DY3) which is an important yellow azo dye used in the industry, is a carcinogen. It was reported that the degradation of DY3 to CO2 is possible by MnP (Spadaro and Renganathan. 1994. Peroxidase-catalyzed oxidation of azo dyes: mechanism of disperse Yellow 3 degradation. Arch Biochem Biophys. 312 (1): 301–307). Another example of environmental pollutants is the class of compounds called chlorophenols. 2,4,6,-Trichlorophenol and pentachlorophenol have been extensively used as wood preservatives and pesticides (Freiter. 1979. Chlorophenols, p 864–872. In “Encylopedia of chemical technology”. Mark, Othmer, Overberger and Seaborg (eds). Vol 5. John Wiley & Sons, Inc. New York, N.Y. and Rappe. 1980. Chloroaromatic compounds containing oxygen, phenols, diphenyl ethers, dibenzo-p-dioxins, and dibenzofuran, p 157–179. In Hutzinger (ed), The handbook for environmental chemistry. Springer-Verlag K G, Berlin, Germany). In addition, 2,4-dichlorophenol and 2,4,5-trichlorophenol are precursors in the synthesis of herbicides (Freiter, supra). It has been reported that the degradation of such persistant environmental pollutants by Phanerochaete chrysosporium involves an initial dechlorination step catalyzed by either LiP or MnP (Reddy et al. 1998. Degradation of 2,4,6-Trichlorophenol by Phanerochaete chrysosporium: Involvement of Reductive Dechlorination; Joshi and Gold. 1993. Degradation of 2,4,5-trichlorophenol by the lignin-degrading basidiomycete Phanerochaete chrysosporium. Appl. Environ. Microbiol. 59:1779–1785; and Valli and Gold. 1991. Degradation of 2,4-dichlorophenol by the lignin-degrading fungus Phanerochaete chrysosporium. J. Bacteriol. 173:345–352).
MnP can also be employed for bioremediation. For example, U.S. Pat. No. 6,268,204 describes how MnP is used to remediate liquid or solid waste streams containing organo-halides.
Fungal MnP is also capable of degrading aminonitrotoluenes, the main intermediates of the explosive 2,4,-trinitrotoluene (TNT). Radioactive experiments using a complex mixture of uniform ring-labeled 14C-TNT reduction products demonstrated the partial direct mineralization of these compounds by manganese peroxidase (Scheibner and Hofrichter. 1998. Conversion of aminonitrotoluenes by fungal manganese peroxidase. J Basic Microbiol. 38(1): 51–59).
MnP can also be employed in the synthesis of phenolic and aromatic amine polymers such as poly(p-ehylphenol) and poly(m-cresol) to help control product yields, molecular weight, molecular weight distribution and polydispersity (U.S. Pat. No. 6,096,859). Such polymers are important constituents of coatings, laminates and intergrated circuit chips. U.S. Pat. No. 5,608,040 reports a process for producing lignin-containing polymers in the presence of radical oxidizing enzymes such as MnP.
Several endeavors for over-expressing MnP in a variety of hosts have been reported. Attempts to express MnP genes in bacteria have resulted in the production of inclusion bodies containing catalytically inactive enzyme. The reason is that prokaryotic organisms such as bacteria inherently lack the ability to synthesize heme, a necessary component of the native enzyme (Andrawis et al. (eds) 1990. Biotechnology in Pulp and Paper Manufacture; Applications and Fundamental Investigations. Butterworth-Heinemann, Butterworth-Heinemann, Boston, 601). Efforts to optimize this system involved refolding of the inactive polypeptides into active enzyme under specific conditions (2 M urea, pH 8.0, in the presence of CaCl2, hemin, and oxidized glutathione) (Whitwam and Tien. 1996. Heterologous expression and reconstitution of fungal Mn peroxidase. Arch Biochem Biophys 15; 333(2):439–46). Still, however, yields were low for large-scale commercial production.
Another system reported for MnP expression is the baculovirus expression system (Pease et al. 1991. Heterologous expression of active manganese peroxidase from Phanerochaete chrysosporium using the baculovirus expression system. Biochem. Biophys. Res. Commun. 179:897–903). This system is capable of producing biochemically active enzyme, indicating proper post-translational modifications, and enzymatic activity could be further enhanced (up to 15-fold increase) upon the addition of hemin at 1 ug/ml to the medium. Still, however, yields are not appreciably higher than those observed in P. chrysosporium cultures. The system also suffers from a serious limitation, its' high production costs. The addition of hemin to the medium is not a cost-effective measure since one gram of hemin crystals can cost about $27.
Expressing MnP in fungal systems also has its pitfalls. Attempts included the expression of exogenous sequences (heterologous expression) as well as the overexpression of endogenous MnP genes (homologous expression). Homologous expression of a recombinant MnP gene was attempted in Phanerochaete chrysosporium. An endogenous MnP gene was placed under the control of the glyceraldehyde-3-phosphate dehydrogenase promoter. Recombinant MnP yields were higher than those of the baculovirus expression systems. Heme insertion, folding, and secretion were normal (Mayfield et al. 1994. Homologous expression of recombinant manganese peroxidase in Phanerochaete chrysosporium. Appl Environ Microbiol. 60(12): 4303–9). Although the expression levels in this system were good enough for structural and functional studies of recombinant MnP, they were not high enough to support cost-effective large-scale industrial production.
Heterologous expression of recombinant MnP in the commercially available fungal systems, Aspergillus oryzae and Aspergillus niger, has also been attempted and shown to be possible. However, success was limited by poor yield and by the small fraction of peroxidase polypeptide that is assembled into a functional enzyme. In the Aspergillus oryzae system, MnP expression was attempted using a vector in which the cDNA of mnp-1 from Phanerochaete chrysosporium was fused with the A. oryzae Taka amylase promoter and secretion signal. Yields of 5 mg rMnP/L were obtained and optimal expression required 500 mg/L hemin in the medium. Lowered concentrations of hemin resulted in decreased yields (Stewart et al. 1996. Efficient expression of a Phanerochaete chrysosporium manganese peroxidase gene in Aspergillus oryzae. Appl. Environ. Microbiol. 62:860–864). In the Aspergillus niger system, overexpression of MnP was unsuccessful. Problems with this system included low specific activity of the recombinant MnP protein, low yields and degradation of a recombinant MnP: GLA fusion protein. The specific activity of rMnP was lower than that of the native enzyme. The initial yields obtained for rMnP in A. niger MGG029 were 5 to 10 mg/liter, which is low compared with other fungal proteins expressed in filamentous fungi. These yields could be increased to 100 mg of extracellular rMnP/liter under hemoglobin supplementation conditions (Conesa et al. 2000. Studies on the production of fungal peroxidases in Aspergillus niger. Appl Environ. Microbiol. 66(7): 3016–23).
The failure of genetically engineered bacterial or fungal systems to produce commercially high levels of MnP has prompted scientists to investigate the plant system. Transgenic plants offer the potential to be one of the most economical systems for large-scale production of proteins for industrial, pharmaceutical, veterinary and agricultural use. Advantages of plant systems include the low cost of growing a large biomass, easy scale-up (increase of planted acreage), natural storage organs (tubers, seeds), and established practices for efficient harvesting, transporting, storing and processing of the plant. Recombinant proteins can be targeted to seeds allowing stable storage of the recombinant proteins for extended periods. Plants offer advantages over other production systems since some proteins may be used without extensive purification, because for many applications, plant material is used directly as a food source or feed stock.
The only example attempting the expression of MnP in plants has failed. Austin et al. report that expressing the P. chrysosporium mnp-1 gene in alfalfa had deleterious effects on plant growth and development in vitro or in the greenhouse. Transgenic alfalfa plants were stunted and flowered later than control plants and the highest-expressing plants, with MnP levels above 0.3% soluble protein, died (Austin et al. 1995. Production and field performance of transgenic alfalfa (Medicago sativa L.) expressing alpha-amylase and manganese-dependent lignin peroxidase. Euphytica 85: 381–93).
The inventors have discovered that it is possible to obtain high level expression of a recombinant, fungally-derived nucleic acid sequence encoding MnP in corn seeds. It is, therefore, an object of the present invention to produce amounts of recombinant MnP (rMnP) that by far exceed the current capacity of traditional recombinant protein sources such as filamentous fungi or bacteria.
A further object of the invention is to produce MnP in plants such that the plant is viable, that is, lives to provide a source of MnP and does not die.
Another object of the invention is the application of large-scale production of MnP to industrial markets for which it had previously been economically unfeasible to enter.
Yet another object of the present invention is to produce rMnP in quantities large enough as to provide considerable cost savings for the industries.
An object of this invention is the development of a plant expression system that allows the efficient and large-scale production of heterologous proteins.
Another object of the invention is to preferentially express the rMnP in the seed of the plant.
A still further object of the invention is to direct expression of rMnP in plants to the cell wall of the plant.
An object of the invention is to further improve expression of rMnP in plants by backcrossing transgenic plants containing the MnP expressing gene into plants with good agronomic traits.
The objectives of this invention will become apparent in the description below. All references cited are incorporated herein by reference.
SUMMARY OF THE INVENTION
Transgenic corn plants and a process of obtaining them in which commercial levels of enzymatically active recombinant manganese peroxidase are produced are shown. Expression vectors are engineered to allow overexpression and accumulation of recombinant manganese peroxidase protein in plant tissue.



DESCRIPTION OF THE DRAWINGS
FIG. 1 is pPGN8997, a construct containing the manganese peroxidase gene, the PGNpr6 promoter, the moPAT marker (maize optimized PAT selectable marker) gene under the control of the CaMV 35S promoter.
FIG. 2 is pPGN8998, which contains the same components as pPGN8997 but also contains the barley alpha-amylase signal sequence (BAASS).
FIG. 3 is pPGN9037 which contains the same components as pPGN8998 except that the globulin 1 promoter is substituted for the PGNpr6 promoter.
FIG. 4 shows a Western blot analysis of corn seed using manganese peroxidase specific antibodies. Seeds are from several T1 MPD events and Hi-II/LH244 control corn. Blank lanes among MPD events reflect the expected expression ratio among T1 seed resulting from outcross of the T0 plants.
FIG. 5 is a graph showing enzymatic activity of rMnP from selected T1 seeds from multiple MPD events and seeds from Hi-II/LH244 wildtype control plants.
FIG. 6 is a Western blot analysis testing the expression of cytoplasmically targeted manganese peroxidase in seed samples from several MPA events.
FIG. 7 is a graph showing the expression based on activity of manganese peroxidase in corn seeds resulting from multiple MPD, MPB and MPA events.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The inventors have determined that expression of enzymatically active manganese peroxidase in plants is feasible and provides substantial advantages over the prior art attempts of producing the enzyme in microorganisms such as bacteria or fungi. According to the present invention, the levels of the enzyme produced in transgenic plants make it economically sound to produce commercial levels of the enzyme. Never before have such high commercially useful concentrations of the enzymes been obtained. Moreover, expression in plants has several advantages. Plants are more economical to grow and can be far more readily produced in large quantities than fungi. In addition, plant material is easy to store and transport.
While expression of manganese peroxidase at levels of about 1% total soluble protein in plant tissue are useful, expression levels of about 10% total soluble protein would allow for a very cost-effective system of commercial production of the MnP in plants.
According to the present invention, the secretion of MnP is a preferred method of expressing the protein at high levels. The inventors have determined that targeting the expression of MnP to the cell wall results in dramatic increases in the amount of MnP expressed in the plant which is correctly folded, and with active enzyme with heme incorporated.
In another preferred embodiment of the present invention, the MnP gene is linked to a promoter which preferentially expressed MnP to the seed of the plant. The inventors have discovered that directing the expression to the seed results in a further dramatic increase in protein accumulation and circumvents plant health problems throughout plant growth.
A combination of directing expression to the cell wall, and preferentially expressing MnP to the seed of the plant results in yet farther increases in expression levels. Expression in plants was typically about 0.5% of total soluble protein of the seed when the protein was expressed in the cytoplasm with a constitutive promoter. When expressed to the cell wall, a six-fold increase was observed. By combining both factors, expression levels up to 15% or a thirty-fold increase were observed.
In accordance with the present invention, a DNA molecule comprising a transformation/expression vector is engineered to incorporate a manganese peroxidase-encoding cDNA. There can be several isozymes for manganese peroxidase each encoded by a separate gene. Some examples are the mnp-1, mnp-2 and mnp-3 from P. chrysosporium (Pease et al. 1989. Manganese-dependent peroxidase from Phanerochaete chrysosporium. Primary structure deduced from cDNA sequence. J. Biol. Chem. 264:13531–35; Pribnow et al. 1989. Characterization of a cDNA encoding a manganese peroxidase, from the lignin-degrading basidiomycete Phanerochaete chrysosporium. J. Biol. Chem. 264:5036–40; Pease and Tien. 1992. Heterogeneity and regulation of manganese peroxidases from Phanerochaete chrysosporium. J Bacteriol. 174(11): 3532–40); MnPL2 from Pleurotus eryngii (Ruiz-Duenas et al. 1999. Heterologous expression of Pleurotus eryngii peroxidase confirms its ability to oxidize Mn2+ and different aromatic substrates. Appli & Environ. Microbiol. 65(10): 4705–07), mnp-2 from Dichomitus squalens (Li et al. 2001. Heterologous expression of a thermostable manganese peroxidase from Dichomitus squalens in Phanerochaete chrysosporium. Arch Biochem Biophys. 385(2): 348–56); and MnPI, MnPII and MnPIII from Phanerochaete sordida (Ruttimann-Johnson et al. 1994. Manganese peroxidases of the white rot fungus Phanerochaete sordida. Appl. Environ. Microbiol. 60(2):599–605). The list of MnP genes here is not intended to be comprehensive but illustrative. The gene used in the present invention is from P. chrysosporium. The cDNA sequence is (SEQ ID NO: 1):










 A  V  C  P   D  G  T   R  V  T   N  A  A  C   C  A  F



 


1
GCAGTCTGTC CAGACGGTAC CCGCGTCACC AACGCGGCGT GCTGCGCTTT


 



CGTCAGACAG GTCTGCCATG GGCGCAGTGG TTGCGCCGCA CGACGCGAAA


 



  I  P  L   A  Q  D  L   Q  E  T   L  F  Q   G  D  C


 


51
CATTCCGCTC GCACAGGACT TGCAAGAGAC TCTGTTCCAG GGTGACTGTG


 



GTAAGGCGAG CGTGTCCTGA ACGTTCTCTG AGACAAGGTC CCACTGACAC


 



G  E  D  A   H  E  V   I  R  L  T   F  H  D   A  I  A


 


101
GCGAAGATGC CCACGAAGTC ATCCGTCTGA CCTTCCACGA CGCTATTGCA


 



CGCTTCTACG GGTGCTTCAG TAGGCAGACT GGAAGGTGCT GCGATAACGT


 



 I  S  Q  S   L  G  P   Q  A  G   G  G  A  D   G  S  M


 


151
ATCTCCCAGA GCCTAGGTCC TCAGGCTGGC GGCGGTGCTG ACGGCTCCAT


 



TAGAGGGTCT CGGATCCAGG AGTCCGACCG CCGCCACGAC TGCCGAGGTA


 



  L  H  F   P  T  I  E   P  N  F   S  A  N   N  G  I


 


201
GCTGCACTTC CCGACAATCG AGCCCAACTT CTCCGCCAAC AACGGCATCG


 



CGACGTGAAG GGCTGTTAGC TCGGGTTGAA GAGGCGGTTG TTGCCGTAGC


 



D  D  S  V   N  N  L   L  P  F  M   Q  K  H   D  T  I


 


251
ATGACTCCGT CAACAACTTG CTTCCCTTCA TGCAGAAACA CGACACCATC


 



TACTGAGGCA GTTGTTGAAC GAAGGGAAGT ACGTCTTTGT GCTGTGGTAG


 



 S  A  A  D   L  V  Q   F  A  G   A  V  A  L   S  N  C


 


301
AGTGCCGCCG ATCTTGTACA GTTCGCCGGT GCGGTCGCGC TGAGCAACTG


 



TCACGGCGGC TAGAACATGT CAAGCGGCCA CGCCAGCGCG ACTCGTTGAC


 



  P  G  A   P  R  L  E   F  M  A   G  R  P   N  T  T


 


351
CCCAGGTGCT CCTCGCCTCG AGTTCATGGC TGGACGTCCG AACACTACCA


 



GGGTCCACGA GGAGCGGAGC TCAAGTACCG ACCTGCAGGC TTGTGATGGT


 



I  P  A  V   E  G  L   I  P  E  P   Q  D  S   V  T  K


 


401
TCCCCGCAGT TGAGGGCCTC ATTCCTGAGC CTCAAGACAG CGTCACCAAA


 



AGGGGCGTCA ACTCCCGGAG TAAGGACTCG GAGTTCTGTC GCAGTGGTTT


 



 I  L  Q  R   F  E  D   A  G  N   F  S  P  F   E  V  V


 


451
ATCCTGCAGC GCTTCGAGGA CGCCGGCAAC TTCTCGCCGT TCGAGGTCGT


 



TAGGACGTCG CGAAGCTCCT GCGGCCGTTG AAGAGCGGCA AGCTCCAGCA


 



  S  L  L   A  S  H  T   V  A  R   A  D  K   V  D  E


 


501
CTCGCTCCTG GCTTCACACA CCGTTGCTCG TGCGGACAAG GTCGACGAGA


 



GAGCGAGGAC CGAAGTGTGT GGCAACGAGC ACGCCTGTTC CAGCTGCTCT


 



T  I  D  A   A  P  F   D  S  T  P   F  T  F   D  T  Q


 


551
CCATCGATGC TGCGCCCTTC GACTCGACAC CCTTCACCTT CGACACCCAG


 



GGTAGCTACG ACGCGGGAAG CTGAGCTGTG GGAAGTGGAA GCTGTGGGTC


 



 V  F  L  E   V  L  L   K  G  T   G  F  P  G   S  N  N


 


601
GTGTTCCTCG AGGTCCTGCT CAAGGGCACA GGCTTCCCGG GCTCGAACAA


 



CACAAGGAGC TCCAGGACGA GTTCCCGTGT CCGAAGGGCC CGAGCTTGTT


 



  N  T  G   E  V  M  S   P  L  P   L  G  S   G  S  D


 


651
CAACACCGGC GAGGTGATGT CGCCGCTCCC ACTCGGCAGC GGCAGCGACA


 



GTTGTGGCCG CTCCACTACA GCGGCGAGGG TGAGCCGTCG CCGTCGCTGT


 



T  G  E  M   R  L  Q   S  D  F  A   L  A  R   D  E  R


 


701
CGGGCGAGAT GCGCCTGCAG TCCGACTTTG CGCTCGCGCG CGACGAGCGC


 



GCCCGCTCTA CGCGGACGTC AGGCTGAAAC GCGAGCGCGC GCTGCTCGCG


 



 T  A  C  F   W  Q  S   F  V  N   E  Q  E  F   M  A  A


 


751
ACGGCGTGCT TCTGGCAGTC GTTCGTCAAC GAGCAGGAGT TCATGGCGGC


 



TGCCGCACGA AGACCGTCAG CAAGCAGTTG CTCGTCCTCA AGTACCGCCG


 



  S  F  K   A  A  M  A   K  L  A   I  L  G   H  S  R


 


801
GAGCTTCAAG GCCGCGATGG CGAAGCTCGC GATCCTCGGC CACAGCCGCA


 



CTCGAAGTTC CGGCGCTACC GCTTCGAGCG CTAGGAGCCG GTGTCGGCGT


 



S  S  L  I   D  C  S   D  V  V  P   V  P  K   P  A  V


 


851
GCAGCCTCAT CGACTGCAGC GACGTCGTCC CCGTCCCGAA GCCCGCCGTC


 



CGTCGGAGTA GCTGACGTCG CTGCAGCAGG GGCAGGGCTT CGGGCGGCAG


 



 N  K  P  A   T  F  P   A  T  K   G  P  K  D   L  D  T


 


901
AACAAGCCCG CGACGTTCCC CGCGACGAAG GGCCCCAAGG ATCTCGACAC


 



TTGTTCGGGC GCTGCAAGGG GCGCTGCTTC CCGGGGTTCC TAGAGCTGTG


 



  L  T  C   K  A  L  K   F  P  T   L  T  S   D  P  G


 


951
ACTCACGTGC AAGGCCCTCA AGTTCCCGAC GCTGACCTCT GACCCCGGTG


 



TGAGTGCACG TTCCGGGAGT TCAAGGGCTG CGACTGGAGA CTGGGGCCAC


 



A  T  E  T   L  I  P   H  C  S  N   G  G  M   S  C  P


 


1001
CTACCGAGAC CCTCATCCCC CACTGCTCCA ACGGCGGCAT GTCCTGCCCT


 



GATGGCTCTG GGAGTAGGGG GTGACGAGGT TGCCGCCGTA CAGGACGGGA


 



 G  V  Q  F   D  G  P   A  .


 


1051
GGTGTTCAGT TCGATGGCCC TGCCTGA


 



CCACAAGTCA AGCTACCGGG ACGGACT






Although the present invention reports the expression of a MnP from P. chrysosporium, other homologous or substantially identical nucleic sequences are contemplated to be capable of being expressed in plants in the same manner. That is, the present invention contemplates any MnP-producing nucleic sequence.
In a preferred embodiment of the invention, expression of high levels of an active enzyme in the plant is accomplished by targeting the enzyme to the cell wall. This may be accomplished by the use of a signal sequence and in a preferred embodiment is the barley alpha amylase signal sequence (Rogers, J. C. 1985. Two barley alpha-amylase gene families are regulated differently in aleurone cells. J. Biol. Chem. 260: 3731–3738). The inventors have discovered that the use of such a localization sequence appears to aid in preventing the cytoplasmic accumulation of truncated forms of manganese peroxidase possibly resulting from pre-mature translation termination, proteolysis, or both.
The methods available for construction of recombinant genes comprising various modifications for improved expression described above can differ in detail. However, the methods generally include the designing and synthesis of overlapping, complementary synthetic oligonucleotides which are annealed and ligated together to yield a gene with convenient restriction sites for cloning. The methods involved are standard methods for a molecular biologist.
Once the gene is engineered to contain desired features, such as the desired localization sequences, it is placed into an expression vector by standard methods. The selection of an appropriate expression vector will depend upon the method of introducing the expression vector into host cells. A typical expression vector contains prokaryotic DNA elements coding for a bacterial replication origin and an antibiotic resistance gene to provide for the growth and selection of the expression vector in the bacterial host; a cloning site for insertion of an exogenous DNA sequence, which in this context would code for manganese peroxidase; eukaryotic DNA elements that control initiation of transcription of the exogenous gene, such as a promoter; and DNA elements that control the processing of transcripts, such as transcription termination/polyadenylation sequences. It also can contain such sequences as are needed for the eventual integration of the vector into the plant chromosome.
In a preferred embodiment, the expression vector also contains a gene encoding a selection marker that is functionally linked to a promoter that controls transcription initiation. For a general description of plant expression vectors and reporter genes, see Gruber et al. 1993. “Vectors for Plant Transformation” in Methods of Plant Molecular Biology and Biotechnology. CRC Press. p 89–119. In a preferred embodiment, the selective gene is a glufosinate-resistance encoding DNA and in another preferred embodiment can be the phosphinothricin acetyl transferase (“PAT”) or maize optimized PAT gene under the control of the CaMV 35S promoter. The gene confers resistance to bialaphos (Gordon-Kamm. 1990. The Plant Cell 2: 603; Uchimiya et al. 1993. Bio/Technology 11: 835; and Anzai et al, 1989. Mol. Gen. Gen. 219: 492).
Promoter elements employed to control expression of MnP and the selection gene, respectively, can be any plant-compatible promoter. Those can be plant gene promoters, such as, for example, the ubiquitin promoter, the promoter for the small subunit of ribulose-1,5-bis-phosphate carboxylase, or promoters from the tumor-inducing plansmids from Agrobacterium tumefaciens, such as the nopaline synthase and octopine synthase promoters or viral promoters such as the cauliflower mosaic virus (CaMV) 19S and 35S promoters or the figwort mosaic virus 35S promoter. See Kay et al. 1987. Duplication of CaMV 35S promoter sequences creates a strong enhancer for plant genes. Science 236: 199–1302 and European patent application No. 0 342 926. See international application WO 91/19806 for a review of illustrative plant promoters suitably employed in the present invention. The range of available plant compatible promoters include tissue specific and inducible promoters. In one embodiment of the present invention, the manganese peroxidase DNA is under the transcriptional control of PGNpr6 promoter. (WO 01/94394). This is a ubiquitin-like promoter, lacking a heat shock element, the sequence of which is set forTH the below.
In a preferred embodiment, a tissue specific promoter is provided to direct transcription of the DNA preferrentially to the seed. Use of such a sequence has been found to considerably increase the expression of MnP. One such promoter is the globulin promoter. This is the promoter of the maize globulin-1 gene, described by Belanger, F. C. and Kriz, A. L. 1991. Molecular Basis for Allelic Polymorphism of the maize Globulin-1 gene. Genetics 129: 863–972. It also can be found as accession number L22344 in the Genbank database. Another example is the phaseolin promoter. See, Bustos et al. 1989. Regulation of B-glucuronidase expression in transgenic tobacco plants by an A/T-rich cis-acting sequence found upstream of a french bean B-phaseolin gene. The Plant Cell. (1): 839–853.
Obviously, many variations on the promoters, selectable markers, signal sequences and other components of the construct are available to one skilled in the art.
In accordance with the present invention, a transgenic plant is produced that contains a DNA molecule, comprised of elements as described above, integrated into its genome so that the plant expresses a heterologous MnP-encoding DNA sequence. In order to create such a transgenic plant, the expression vectors containing the gene can be introduced into protoplasts, into intact tissues, such as immature embryos and meristems, into callus cultures, or into isolated cells. Preferably, expression vectors are introduced into intact tissues. General methods of culturing plant tissues are provided, for example, by Miki et al. 1993. “Procedures for Introducing Foreign DNA into Plants” in Methods in Plant Molecular Biology and Biotechnology, Glick et al (eds) CRC Press pp. 67–68 and by Phillips et al. 1988 “Cell/Tissue Culture and In Vitro Manipulation” in Corn and Corn Improvement 3d Edit. Sprague et al (eds) American Soc. of Agronomy pp. 345–387. The selectable marker incorporated in the DNA molecule allows for selection of transformants.
Methods for introducing expression vectors into plant tissue available to one skilled in the art are varied and will depend on the plant selected. Procedures for transforming a wide variety of plant species are well known and described throughout the literature. See, for example, Miki et al, supra; Klein et al. 1992. Bio/Technology 10:26; and Weisinger et al. 1988. Ann. Rev. Genet. 22: 421–477. For example, the DNA construct maybe introduced into the genomic DNA of the plant cell using techniques such as microprojectile-mediated delivery (Klein et al. 1987. Nature 327: 70–73); electroporation (Fromm et al. 1985. Proc. Natl. Acad. Sci. 82: 5824); polyethylene glycol (PEG) precipitation (Paszkowski et al. 1984. Embo J. 3: 2717–272); direct gene transfer (WO 85/01856 and EP No. 0 275 069); in vitro protoplast transformation (U.S. Pat. No. 4,684,611) and microinjection of plant cell protoplasts or embryogenic callus (Crossway, 1985. Mol. Gen. Genetics 202:179–185). Co-cultivation of plant tissue with Agrobacterium tumefaciens is another option, where the DNA constructs are placed into a binary vector system (Ishida et al. 1996. “High Efficiency Transformation of Maize (Zea mays L.) Mediated by Agrobacterium tumefaciens”. Nature Biotechnology 14:745–750). The virulence functions of the Agrobacterium tumefaciens host will direct the insertion of the construct into the plant cell DNA when the cell is infected by the bacteria. See, for example Horsch et al. 1984. Science 233: 496–498, and Fraley et al. 1983. Proc. Natl. Acad. Sci. 80: 4803.
Standard methods for transformation of canola are described by Moloney et al. 1989. “High Efficiency Transformation of Brassica napus Using Agrobacterium Vectors” Plant Cell Reports 8:238–242. Corn transformation is described by Fromm et al, 1990. Bio/Technology 8:833 and Gordon-Kamm et al, supra. Agrobacterium is primarily used in dicots, but certain monocots such as maize can be transformed by Agrobacterium. U.S. Pat. No. 5,550,318. Rice transformation is described by Hiei et al. 1994. “Efficient Transformation of Rice (Oryza sativs L.) Mediated by Agrobacterium and Sequence Analysis of the Boundaries of the T-DNA” The Plant Journal 6(2): 271–282, Christou et al. 1992. Trends in Biotechnology 10:239 and Lee et al. 1991. Proc. Nat'l Acad. Sci. USA 88:6389. Wheat can be transformed by techniques similar to those used for transforming corn or rice. Sorghum transformation is described by Casas et al., 1997. Transgenic sorghum plants obtained after microprojectile bombardment of immature inflorescences. In vitro cellular and developmental biology, Plant. 33:92–100 and by Wan et al. 1994. Plant Physiology. 104:37. Soybean transformation is described in a number of publications, including U.S. Pat. No. 5,015,580.
In one preferred method, the Agrobacterium transformation methods of Ishida supra and also described in U.S. Pat. No. 5,591,616, are generally followed, with modifications that the inventors have found improve the number of transformants obtained. The Ishida method uses the A188 variety of maize that produces Type I callus in culture. In one preferred embodiment the High II maize line is used which initiates Type II embryogenic callus in culture. While Ishida recommends selection on phosphinothricin when using the bar or PAT gene for selection, another preferred embodiment provides for use of bialaphos instead.
The bacterial strain used in the Ishida protocol is LBA4404 with the 40 kb super binary plasmid containing three vir loci from the hypervirulent A281 strain. The plasmid has resistance to tetracycline. The cloning vector cointegrates with the super binary plasmid. Since the cloning vector has an E. coli specific replication origin, but not an Agrobacterium replication origin, it cannot survive in Agrobacterium without cointegrating with the super binary plasmid. Since the LBA4404 strain is not highly virulent, and has limited application without the super binary plasmid, the inventors have found in yet another embodiment that the EHA101 strain is preferred. It is a disarmed helper strain derived from the hypervirulent A281 strain. The cointegrated super binary/cloning vector from the LBA4404 parent is isolated and electroporated into EHA 101, selecting for spectinomycin resistance. The plasmid is isolated to assure that the EHA101 contains the plasmid.
Further, the Ishida protocol as described provides for growing fresh culture of the Agrobacterium on plates, scraping the bacteria from the plates, and resuspending in the co-culture medium as stated in the '616 patent for incubation with the maize embryos. This medium includes 4.3 g MS salts, 0.5 mg nicotinic acid, 0.5 mg pyridoxine hydrochloride, 1.0 ml thiamine hydrochloride, casamino acids, 1.5 mg 2,4-D, 68.5 g sucrose and 36 g glucose, all at a pH of 5.8. In a further preferred method, the bacteria are grown overnight in a 1 ml culture, then a fresh 10 ml culture re-inoculated the next day when transformation is to occur. The bacteria grow into log phase, and are harvested at a density of no more than OD600=0.5 and is preferably between 0.2 and 0.5. The bacteria are then centrifuged to remove the media and resuspended in the co-culture medium. Since Hi-II is used, medium preferred for Hi-II is used. This medium is described in considerable detail by Armstrong, C. I. and Green C. E. 1985. Establishment and maintenance of friable, embryogenic maize callus and involvement of L-proline. Planta 154:207–214. The resuspension medium is the same as that described above. All further Hi-II media are as described in Armstrong et al. The result is redifferentiation of the plant cells and regeneration into a plant. Redifferentiation is sometimes referred to as dedifferentiation, but the former term more accurately describes the process where the cell begins with a form and identity, is placed on a medium in which it loses that identity, and becomes “reprogrammed” to have a new identity. Thus the scutellum cells become embryogenic callus.
It is preferred to select the highest level of expression of MnP, and it is thus useful to ascertain expression levels in transformed plant cells, transgenic plants and tissue specific expression. One such method is to measure the expression of the target protein as a percentage of total soluble protein. One standard assay is the Bradford assay which is well known to those skilled in the art (Bradford, M. 1976. Anal. Biochem. 72:248). The biochemical activity of the recombinant protein should also be measured and compared with a wildtype standard. The activity of MnP can be determined by the methods described in Wariishi et al. 1992. Manganese(II) oxidation by manganese peroxidase from the basidiomycete Phanerochaete chrysosporium. Kinetic mechanism and role of chelators. J. Biol. Chem. 267:23688–23695.
The levels of expression of the gene of interest can be enhanced by the stable maintenance of a MnP encoding gene on a chromosome of the transgenic plant. Use of linked genes, with herbicide resistance in physical proximity to the MnP gene, would allow for maintaining selective pressure on the transgenic plant population and for those plants where the genes of interest are not lost.
Backcrossing methods may be used to introduce the gene into other plants. This is desirable when, for example, the gene is introduced into a plant hybrid, inbred, or variety that is easily transformed, but does not have good agronomic characteristics. Through backcrossing, the gene can be introduced into plants with good agronomic characteristics and/or characteristics that provide for better expression of the gene. This technique has been used for decades to introduce traits into a plant. An example of a description of this and other plant breeding methodologies that are well known can be found in references such as “Plant Breeding Methodology” edit. Neal Jensen, John Wiley & Sons, Inc. (1988). In a typical backcross protocol, the original variety of interest (recurrent parent) is crossed to a second variety (nonrecurrent parent) that carries the single gene of interest to be transferred. The resulting progeny from this cross are then crossed again to the recurrent parent and the process is repeated until a plant is obtained wherein essentially all of the desired morphological and physiological characteristics of the recurrent parent are recovered in the converted plant, in addition to the single transferred gene from the nonrecurrent parent.
With transgenic plants according to the present invention, MnP can be produced in commercial quantities. Thus, the selection and propagation techniques described above yield a plurality of transgenic plants that are harvested in a conventional manner. The plant seed expressing the recombinant MnP can be used in a commercial process, or the MnP extracted. When using the seed itself, it can, for example, be made into flour and then applied in the commercial process. MnP extraction from biomass can be accomplished by known methods. Downstream processing for any production system refers to all unit operations after product synthesis, in this case protein production in transgenic seed (Kusnadi, A. R., Nikolov, Z. L., Howard, J. A., 1997. Biotechnology and Bioengineering. 56:473–484). Seed is processed either as whole seed ground into flour, or fractionated and the germ separated from the hulls and endosperm. If germ is used, it is usually defatted using a hexane extraction and the remaining crushed germ ground into a meal or flour. In some cases the germ is used directly in the industrial process or the protein can be extracted (See, e.g. WO 98/39461). Extraction is generally made into aqueous buffers at specific pH to enchance recombinant protein extraction and minimize native seed protein extraction. Subsequent protein concentration or purification can follow. In the case of industrial enzymes, concentration through membrane filtration is usually sufficient.
The enzyme can be used in a number of different industrial processes. Examples include bleaching of lignocellulosic kraft pulps by a process employing a sequential reaction of oxidative enzymes, such as MnP, and hydrogen peroxide. The process is described in U.S. Pat. No. 5,691,193. Briefly, it is a three step process that involves non-chlorine chemicals. The first step is the oxidation of kraft pulp with MnP in the presence of Mn(II) salts, chelator and hydrogen peroxide. The subsequent two steps comprise the chelation of metals in the pulp and alkaline hydrogen peroxide treatment. This use of MnP is an improvement over the current use of chlorine for depolymerization of lignin, which leads to the production of chlorinated aromatic compounds, which are an environmentally undesirable by-product of paper mills. MnP is also used for pulping processes. One example is given by U.S. Pat. No. 6,267,841 to a process of low energy thermomechanical pulping which employs treatment of the pulp with MnP between refining zones.
Another example lies in the field of bioremediation. Remediation of liquid or solid waste streams containing organo-halides is possible by a process described in U.S. Pat. No. 6,268,204. This process employs MnP to degrade halogenated aromatic compounds followed by forcing the products through a semi-permeable membrane partition.
Another use of MnP is in the synthesis of phenolic and aromatic amine polymers that are constituents of coatings, laminates and integrated circuit chips. Examples of such polymers include poly(p-ethylphenol) and poly(m-cresol). There is a need in the industrial synthesis of such compounds to control product yields, molecular weight, molecular weight distribution and polydispersity of the polymer molecules. U.S. Pat. No. 6,096,859 describes how such parameters may be controlled by a process employing peroxidases such as MnP. Another use for MnP in a manufacturing process is described in U.S. Pat. No. 5,608,040. The process is for producing lignin-containing polymers and comprises a polymerization step carried out in the presence of a radical oxidizing enzyme such as MnP. These are but few of the many uses to which the enzyme may be put.
The following illustrates, but is not intended to limit the scope of the invention. It will be evident to one skilled in the art that variations and modifications are possible and fall within the scope and spirit of the invention.
EXAMPLE 1
Preparation of Plasmids
In overview, seed from Hi-II maize kernels were transformed with constructs comprising elements according to the present invention. The constructs are designated pPGN8997, pPGN8998 and pPGN9037. The pPGN8997 construct comprises the PGNpr6 promoter, a MnP encoding sequence, PinII terminator sequences and the 35S promoter and terminator with moPAT (maize optimized PAT selectable marker). The pPGN8998 construct comprises the same elements as pPGN8997 except that the MnP encoding sequence has the barley alpha amylase export signal sequence. Construct pPGN9037 has the same elements as pPGN8998 except that the PGNpr6 promoter was substituted by the Globulin 1 promoter.
A vector containing a cDNA for MnP and a fungal secretion signal has been described before; see Stewart et al. 1996. Efficient expression of a Phanerochaete chrysosporium manganese peroxidase gene in Aspergillus olyzae. Appl. Environ. Microbiol. 62:860–864. The secretion signal was either removed to give manganese peroxidase without a signal sequence in one case (pPGN8997-see FIG. 1) or replaced by the barley alpha amylase signal sequence (BAASS) in another case (pPGN8998-see FIG. 2). For the construction of pPGN8997 an NcoI restriction site containing the sequence necessary for the initiating methionine codon was added to the 5′ end of the cDNA using polymerase chain reaction (PCR). This resulted in the MnP sequence without a signal sequence. For pPGN8998, the BAASS, which contains an NcoI site and the initiating methionine codon, was added to the 5′ end of the cDNA using PCR resulting in a BAASS:manganese peroxidase construct. An HpaI restriction site was added to the 3′ end of the cDNA using PCR. The resulting NcoI-HpaI fragments, either manganese peroxidase alone or BAASS:manganese peroxidase were ligated into the BbsI-HpaI vector fragment from pPGN2774 which contains the ubiquitin-like promoter and the Pin II terminator sequences resulting in plasmids K2686 or K2704 respectively. The HindIII-NcoI ubiquitin-like promoter fragment from both K2686 and K2704 were removed and replaced with the HindIII-NcoI fragment from pPGN7583 which contains the PGNpr6 promoter (WO 01/94394) resulting in K2792 and K2781 respectively. This modified ubiquitin-like promoter lacks a 5′ heat shock sequence and is set forth below (SEQ ID NO: 2):








gtgcagcgtgacccggtcgtgcccctctctagagataatgagcattgcatgtctaagttataaaaaattaccacatattttttttgtcaca



 


cttgtttgaagtgcagtttatctatctttatacatatatttaaacttactctacgaataatataatctatagtactacaataatatcagtgtttta


 


gagaatcatataaatgaacagttagacatggtctaaaggacaattgagtattttgacaacaggactctacagttttatctttttagtgtgc


 


atgtgttctcctttttttttgcaaatagcttcacctatataatacttcatccattttattagtacatccatttagggtttagggttaatggtttttat


 


agactaatttttttagtacatctattttattctattttagcctctaaattaagaaaactaaaactctattttagtttttttatttaataatttagatata


 


aaatagaataaaataaagtgactaaaaattaaacaaataccctttaagaaattaaaaaaactaaggaaacatttttcttgtttcgagtag


 


ataatgccagcctgttaaacgccgtcgacgagtctaacggacaccaaccagcgaaccagcagcgtcgcgtcgggccaagcgaa


 


gcagacggcacggcatctctgtcgctgcctctcgagagttccgctccaccgttggacttgctccgctgtcggcatccagaaattgc


 


gtggcggagcggcagacgtgagccggcacggcaggcggcctcctcctcctctcacggcacggcagctacgggggattcctttc


 


ccaccgctccttcgctttcccttcctcgcccgccgtaataaatagacaccccctccacaccctctttccccaacctcgtgttgttcgga


 


gcgcacacacacacaaccagatctcccccaaatccacccgtcggcacctccgcttcaaggtacgccgctcgtcctcccccccccc


 


ccctctctaccttctctagatcggcgttccggtccatggttagggcccggtagttctacttctgttcatgtttgtgttagatccgtgtttgtg


 


ttagatccgtgctgctagcgttcgtacacggatgcgacctgtacgtcagacacgttctgattgctaacttgccagtgtttctctttgggg


 


aatcctgggatggctctagccgttccgcagacgggatcgatttcatgattttttttgtttcgttgcatagggtttggtttgcccttttccttta


 


tttcaatatatgccgtgcacttgtttgtcgggtcatcttttcatgcttttttttgtcttggttgtgatgatgtggtctggttgggcggtcgttcta


 


gatcggagtagaattctgtttcaaactacctggtggatttattaattttggatctgtatgtgtgtgccatacatattcatagttacgaattga


 


agatgatggatggaaatatcgatctaggataggtatacatgttgatgcgggttttactgatgcatatacagagatgctttttgttcgcttg


 


gttgtgatgatgtggtgtggttgggcggtcgttcattcgttctagatcggagtagaatactgtttcaaactacctggtgtatttattaatttt


 


ggaactgtatgtgtgtgtcatacatcttcatagttacgagtttaagatggatggaaatatcgatctaggataggtatacatgttgatgtg


 


ggttttactgatgcatatacatgatggcatatgcagcatctattcatatgctctaaccttgagtacctatctattataataaacaagtatgtt


 


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ttggtactgtttcttttgtcgatgctcaccctgttgtttggtgttacttctgca






The HindIII-NotI fragment from K2792 or K2781 was then ligated into the HindIII-Not vector PGN8916, which contains the 35S:PAT, resulting in PGN8997 (manganese peroxidase alone) or PGN8998 (BAASS:manganese peroxidase) respectively. To generate plasmid pPGN9037 (FIG. 3), the NcoI-NotI fragment from K2781 containing BAASS:manganese peroxidase along with the HindIII-NcoI fragment from KB381 containing the Globulin 1 promoter were ligated into the HindIII-NotI vector backbone from PGN8916 resulting in the final GlobulinI:BAASS:manganese peroxidase vector PGN9037. Constructs were sequenced to confirm that no errors were introduced during cloning procedures.

EXAMPLE 2
Transformation of Maize
Fresh immature zygotic embryos were harvested from Hi-II maize kernels at 1–2 mm in length. The general methods of Agrobacterium transformation were used as described by Japan Tobacco, at Ishida et al. 1996. “High efficiency transformation of maize (Zea mays L.) mediated by Agrobacterium tumefaciens” Nature Biotechnology 14:745–750 with the modifications described supra. Fresh embryos were treated with 0.5 ml log phase Agrobacterium strains EHA 101. Bacteria were grown overnight in a rich medium with kanamycin and spectinomycin to an optical density of 0.5 at 600 nm, pelleted, then re-inoculated in a fresh 10 ml culture. The bacteria were allowed to grow into log phase and were harvested at no more dense than OD600=0.5. The bacterial culture is resuspended in a co-culture medium.
For stable transformations, embryos were transferred to a bialaphos selective agent on embryogenic callus medium and transferred thereafter every two weeks to allow growth of transformed type II callus. Plants were regenerated from the callus. Those events resulting from the transformation of plants with the pPGN8997 vector are referred to as MPA events. Those resulting from pPGN8998 transformation are MPB events and those from pPGN9037 events are MPD events.
EXAMPLE 3
Manganese Peroxidase Analysis
T1 seeds of transgenic maize plants were analyzed by a MnP activity assay. Transgenic maize seed samples were homogenized individually with a custom seed pulverizer or in bulks of 50 seeds in a coffee grinder and extracted in 50 mM sodium tartrate pH 4.5. Protein concentration of the extracts was determined by the method of Bradford, with BSA as standard (Bradford, M. 1976. Anal. Biochem. 72:248). MnP activity in the extracts was measured by monitoring the oxidation of 2,6-dimethoxyphenol at 469 nm (Wariishi et al. 1992. Manganese(II) oxidation by manganese peroxidase from the basidiomycete Phanerochaete chrysosporium. Kinetic mechanism and role of chelators. J. Biol. Chem. 267: 23688–23695). Briefly, 0.2–10 microgram of seed extract was assayed at 28° C. for 5 minutes in 50 mM tartrate pH 4.5 containing 0.5 mM manganese sulfate, 1 mM 2,6-dimethoxphenol, and 0.05 mM hydrogen peroxide. Levels of MnP expressed in the extracts were reported as a percent of total soluble protein (% TSP).
To test the expression of MnP in corn seed, protein extracts were prepared from individual T1 seed of several MPD events and Hi-II/LH244 control corn. Using a manganese peroxidase-specific antibody, the full-length fungal enzyme was detected by immunoblot analysis for the transgenic individuals, while no product was seen in the control corn (see FIG. 4). Western analysis is a well known technique to those skilled in the art. This common procedure involves isolating the protein of interest and placing it on an acrylamide gel. The protein is then blotted onto a membrane and contacted with a labeling substance. See for example, Hood et al. 1997. Commercial Production of Avidin from Transgenic Maize; Characterization of Transformants, Production, Processing, Extraction and Purification. Molecular Breeding 3:291–306.
To determine whether the recombinant MnP proteins were enzymatically active, extracts from T1 seed transformed with the pPGN9037 construct (called MPD events) were analyzed by the methods of Wariishi, described supra. Compared to the Hi-II/LH244 (wildtype corn) control, a large increase in manganese-dependent enzyme activity was seen (FIG. 5), indicating that the heterologous MnP fungal enzyme was successfully expressed in corn seed. The inventors have found that protein extracts from seeds of MPA events (ie containing the pPGN9887 construct which does not have the BAASS signal sequence) had very low to negligible enzymatic activity (data not shown). Such extracts were further subjected to immunoblot analysis. Results (FIG. 6) indicate that none of the samples expressed detectable levels of full-length polypeptide. However, two smaller bands were detected. These bands likely represent truncated forms of MnP, possibly resulting from pre-mature translation termination, proteolysis, or both. This indicates that cytoplasmically-targeted MnP is truncated and that the secretion of MnP is a key element in successful overexpression and accumulation of enzymatically active protein.
To compare the effects of different promoters and targeting on MnP accumulation in plant tissues, levels of MnP in seeds were determined as described, supra. Five individual seeds from ten different ears per transgenic event were analyzed and the highest single seed is reported for each plant. The highest single seed for constructs pPGN8997, pPGN8998 and pPGN9037 were plotted. As shown in FIG. 7, the highest-expressing seeds which had, on average, MnP levels at 15% TSP were from plants transformed with pPGN9037. Seeds from transgenic plants with pPGN8998 had MnP expression levels up to an average of 3% TSP and those from transgenic plants with pPGN8997 had MnP levels of less than 0.3% TSP. This clearly indicates that the secretion of the protein to the cell wall correlates with accumulation of high MnP levels. Preferential expression of the protein to the seed of the plant also results in increased MnP accumulation. It was found by the inventors that the use of a seed-preferred promoter (such as the Globulin 1 promoter) not only results in dramatic increases in accumulation over that of a constitutive promoter (such as PGNpr6 promoter), but also circumvents plant health problems observed throughout plant growth.
It is not necessary to extract the protein from the plant tissue, which instead can be used in direct application. Where it is extraction is desired, use of phosphate buffered saline with Tween (PBST) buffer is the default extraction method for initial screening of proteins, particularly when performing ELISA assays for quantification. However, for enzyme assays, the buffer is critical to enzyme activity detection, and PBST is not usually appropriate. Therefore, to improve quantification of the enzyme in corn seed extract, the seed was extracted in tartrate buffer, tartrate being one of the substrates of the manganese peroxidase enzyme. Estimates of recombinant protein yield per dry weight when proteins are extracted with PBST are approximately 100 fold less than their calculated percent of TSP. Tartrate buffer extracts four-fold less corn protein, though it has no effect on the solubility of the manganese peroxidase. Therefore, when MP is 15% of soluble protein in tartrate buffer, the estimate on a dry weight basis is approximately 0.0375%. (This is a single high seed value recovered several times in the T1 generation). Thus, particularly when using the tartrate buffer for extraction, improving expression levels even further through plant breeding techniques is desriable, as described below, is most useful.
EXAMPLE 4
Increasing Expression Levels Through Breeding
The Hi-II maize line that is used in tissue culture for plant transformation shows poor agronomic characteristics and is not high-yielding in the field. However, one of the most important goals for industrial protein production is yield near that of commercial corn lines. Thus, agronomic quality of early transgenic material can be improved through breeding the transgenic plant into plants with improved agronomic characteristics and/or which have chacteristics that provide for improved expression of the enzyme. To accomplish this, T1 seed from selected high-MnP-expressing independent lines was planted in nurseries and crossed to elite inbreds. The goal is to develop high-yielding hybrids with good agronomic qualities. Improved expression levels are expected by breeding into elite varities using the backcrossing methods described, supra.
Crossing the Hi-II events with Stiff Stalk elite germplasm in particular can also increase event recovery. (See U.S. Ser. No. 10/349,392, to be published; Horn, Michael E.; Harkey, Robin L.; Vinas, Amanda K.; Drees, Carol F.; Barker, Donna K.; and Lane, Jeffrey R., “Use of Hill-Elite Hybrids in Agrobacterium-based Transformation of Maize” In Vitro Cell. Dev. Biol.-Plant. (In press)). Stiff Stalk inbreds have been available since at least about the 1950s and are derived from the Iowa Stiff Stalk synthetic population. Sprague, G. F. “Early testing of inbred lines of maize” J. Amer. Soc. Agron. (1946)38:108–117; for examples see PI accession no. 550481 and discussion of Stiff Stalk germplasm at U.S. Pat. Nos. 5,706,603; 6,252,148; 5,245,975; 6,344,599; 5,134,074; and Neuhausen, S. “A survey of Iowa Stiff Stalk parents derived inbreds and BSS(HT)C5 using RFLP analysis” MNL (1989)63: 110–111.
In this instance, the transgenic plant was crossed into one of two different elite Stiff Stalk elite plants, SP114 or SP112. Improved expression of MnP of ten times levels achieved in Hi-II is expected. In each generation, the highest expressing ears showing agronomic promise are selected and seed replanted from those ears in subsequent nurseries. After pollination, maturation and harvest, 50 seed from each progeny ear are combined, ground and analyzed for expression levels of extractable laccase. Only those showing improvement in the amount of MnP are selected for replanting. At each generation, approximately the top 10% of lines are replanted for the breeding program.
Levels of enzymatically active MnP that are produced in transgenic plants are commercially very attractive. Levels of 15% TSP are considerably higher than those obtained by conventional means. For example, such levels can allow the recovery of up to 0.04%–0.15% dry weight in a single T1 seed and 0.02% dry weight in T2 ear bulks. 0.15% dry weight is roughly equivalent to 1–5 g/L of enzyme produced in fungal fermentation. (see table below).







TABLE 1







Expression levels required to reach cost targets for industrial enzymes


in fungal fermentation and corn seed expression systems.









Required expression level of industrial enzyme (IE)









Cost/kg a.i. IE
Fungal fermentation
Unpurified from corn seed





$1,000
 1 g/L 
0.02% dry weight


$100  
 10 g/L 
 0.2% dry weight


$10  
100 g/L**
  2% dry weight





**Not practical






Before this invention, the maximum amount of rMnP reported was 0.05–0.1 g/L in the Aspergillus niger expression system and at higher amounts, the fungi did not survive. Even under hemin supplementation conditions, this amount could only be increased to 0.1 g/L. Cost efficiency for purposes of commercial production indicates at least 1 g/L is preferable, equivalent to about 0.1% dry weight of total soluble protein in corn seed, or about 10% total soluble protein. While levels at about 0.01% of dry weight (about 1% total soluble protein) are useful, expression levels of 0.1% dry weight (about 10% total soluble protein) would be commercially attractive, as it would allow recovery of 1 g active ingredient from 1 kg of corn. Therefore, this invention allows the production of MnP amounts that far exceed the current capacity of traditional recombinant protein sources such as filamentous fungi or bacteria. Thus it is evident that the invention accomplishes at least all of its objectives.

## Claims

1. A viable corn plant expressing manganese peroxidase, wherein the manganese peroxidase is preferentially directed to the cell wall of the plant.

2. Seeds of the plant of claim 1 expressing manganese peroxidase.

3. A Plant cells of a corn plant expressing manganese peroxidase such that the manganese peroxidase is preferentially directed to the cell wall and the plant cells is viable.

4. The plant of claim 1 wherein the manganese peroxidase is expressed at levels of at least about 0.1% total soluble protein.

5. The plant of claim 4 wherein the manganese peroxidase protein is expressed at levels of at least about 3.0% total soluble protein.

6. The plant of claim 5 wherein the manganese peroxidase protein is expressed at levels of at least about 10% total soluble protein.

7. The plant of claim 5 wherein the manganese peroxidase protein is expressed at levels of at least about 15% total soluble protein.

8. The plant of claim 1 further comprising a promoter preferentially directing expression of the manganese peroxidase to the seed of the plant.

9. A method for expressing manganese peroxidase in a viable corn plant comprising expressing in a corn plant cell a nucleic acid construct comprising a sequence encoding a manganese peroxidase protein, wherein the manganese peroxidase is preferentially directed to the cell wall.

10. The method of claim 9 further comprising operably linking with the nucleic acid construct a nucleotide sequence preferentially directing expression to the seed of the plant.

11. A method for producing increased levels of manganese peroxidase in a corn plants comprising:
(i) expressing in a corn plant tissue a first nucleotide sequence encoding a manganese peroxidase protein and a second nucleotide sequence operably linked to the first nucleotide sequence and which preferentially directs expression of the first nucleotide sequence to the cell wall of the plant tissue;
(ii) culturing a plant from the plant tissue;
(iii) growing and harvesting the plant such that manganese peroxidase is expressed.

12. The method of claim 11 further comprising a third nucleotide sequence preferentially directing expression of the first nucleotide sequence to the seed of the plant.

13. The method of claim 11 wherein the manganese peroxidase is expressed at levels of at least about 0.1% total soluble protein or more.

14. The method of claim 13 wherein the manganese peroxidase is expressed at levels of at least about 3% total soluble protein or more.

15. The method of claim 14 wherein the manganese peroxidase is expressed at levels of at least about 10% total soluble protein or more.

16. A method of producing manganese peroxidase at levels of at least about 0.1% total soluble protein, comprising providing biomass from a plurality of corn plants, of which at least certain plants contain a nucleotide molecule comprising a heterologous nucleotide sequence coding for the manganese peroxidase, wherein the nucleotide sequence is operably linked to a nucleotide sequence preferentially directing of the manganese peroxidase to the cell wall of the certain plants to produce manganese peroxidase expressed at levels of at least about 0.1% total soluble protein.

17. The plant of claim 1 expressing manganese peroxidase at levels of at least 0.3% total soluble protein.

18. The method of claim 9 comprising expressing manganese peroxidase at levels of at least about 0.1% total soluble protein in said plant.

19. The method of claim 9 comprising expressing manganese peroxidase at levels of at least about 0.3% total soluble protein in said plant.

20. The method of claim 9 comprising expressing manganese peroxidase at levels of at least about 1% total soluble protein in said plant.

21. The method of claim 9 comprising expressing manganese peroxidase at levels of at least about 3% total soluble protein.

22. The method of claim 9 comprising expressing manganese peroxidase at levels of at least about 10% total soluble protein.

23. The method of claim 9 comprising expressing manganese peroxidase at levels of at least about 15% total soluble protein.