bluuebunny/crossref_metadata_2025_split huggingface dataset:
Initiation of silencing of maize MuDR/Mu transposable elements
Authors: Rudenko George N. , Ono Akemi , Walbot Virginia 
Published: December 2004

SummaryHomology‐dependent gene silencing contributes to genomic stability through suppression of transposable elements. Co‐ordinate epigenetic silencing is the main regulatory mechanism controlling dispersed, multicopy MuDR/Mu elements responsible for Mutator activity in maize. Silencing eliminates transposition and proceeds through transcriptional inactivation of MuDR genes and DNA methylation of the terminal inverted repeats (TIRs) in both the regulatory MuDR and non‐autonomous Mu elements. In plants with active MuDR/Mu elements, initiation of silencing coincides with nuclear retention of non‐polyadenylated RNA derived from MuDR and recently described MuDR homologs (hMuDR elements). Nuclear accumulation of MuDR/hMuDR RNA is developmentally progressive, paralleling loss of Mutator activity and is predictive of loss of Mu somatic excision in the progeny. A high ratio of nuclear to cytoplasmic RNA is the earliest molecular marker for MuDR silencing suggesting that the nuclear RNA may trigger transcriptional silencing. We also demonstrate the constitutive presence of small transposon‐specific RNAs of 21–26 nucleotides in all maize lines tested, independent of the Mutator activity. The role of the small RNAs in transposon silencing and translational regulation of transposon‐encoded proteins is discussed.
Identification of photorespiratory glutamate:glyoxylate aminotransferase (GGAT) gene in Arabidopsis
Authors: Igarashi Daisuke , Miwa Tetsuya , Seki Motoaki , Kobayashi Masatomo , Kato Tomohiko , Tabata Satoshi , Shinozaki Kazuo , Ohsumi Chieko 
Published: December 2004

SummaryIn the photorespiratory process, peroxisomal glutamate:glyoxylate aminotransferase (GGAT) catalyzes the reaction of glutamate and glyoxylate to 2‐oxoglutarate and glycine. Although GGAT has been assumed to play important roles for the transamination in photorespiratory carbon cycles, the gene encoding GGAT has not been identified. Here, we report that an alanine:2‐oxoglutarate aminotransferase (AOAT)‐like protein functions as GGAT in peroxisomes. Arabidopsis has four genes encoding AOAT‐like proteins and two of them (namely AOAT1 and AOAT2) contain peroxisomal targeting signal 1 (PTS1). The expression analysis of mRNA encoding AOATs and EST information suggested that AOAT1 was the major protein in green leaves. When AOAT1 fused to green fluorescent protein (GFP) was expressed in BY‐2 cells, it was found to be localized to peroxisomes depending on PTS1. By screening of Arabidopsis T‐DNA insertion lines, an AOAT1 knockout line (aoat1‐1) was isolated. The activity of GGAT and alanine:glyoxylate aminotransferase (AGAT) in the above‐ground tissues of aoat1‐1 was reduced drastically and, AOAT and glutamate:pyruvate aminotransferase (GPAT) activity also decreased. Peroxisomal GGAT was detected in the wild type but not in aoat1‐1. The growth rate was repressed in aoat1‐1 grown under high irradiation or without sugar, though differences were slight in aoat1‐1 grown under low irradiation, high‐CO2 (0.3%) or high‐sugar (3% sucrose) conditions. These phenotypes resembled those of photorespiration‐deficient mutants. Glutamate levels increased and serine levels decreased in aoat1‐1 grown in normal air conditions. Based on these results, it was concluded that AOAT1 is targeted to peroxisomes, functions as a photorespiratory GGAT, plays a markedly important role for plant growth and the metabolism of amino acids.
Phospholipase C is required for the control of stomatal aperture by ABA
Authors: Hunt Lee , Mills Lewis N. , Pical Christophe , Leckie Calum P. , Aitken Fiona L. , Kopka Joachim , Mueller‐Roeber Bernd , McAinsh Martin R. , Hetherington Alistair M. , Gray Julie E. 
Published: December 2004

SummaryThe calcium‐releasing second messenger inositol 1,4,5‐trisphosphate is involved in the regulation of stomatal aperture by ABA. In other signalling pathways, inositol 1,4,5‐trisphosphate is generated by the action of phospholipase C. We have studied the importance of phospholipase C in guard cell ABA‐signalling pathways. Immunolocalisation of a calcium‐activated phospholipase C confirmed the presence of phospholipase C in tobacco guard cells. Transgenic tobacco plants with considerably reduced levels of phospholipase C in their guard cells were only partially able to regulate their stomatal apertures in response to ABA. These results suggest that phospholipase C is involved in the amplification of the calcium signal responsible for reductions in stomatal aperture in response to ABA. As full ABA‐induced inhibition of stomatal opening was not observed, our results support a role for the action of other calcium‐releasing second messengers in the guard cell ABA‐signalling pathway. It is not known whether these different calcium‐releasing second messengers act in the same or parallel ABA‐signalling pathways.
Stress‐induced somatic embryogenesis in vegetative tissues of Arabidopsis thaliana
Authors: Ikeda‐Iwai Miho , Umehara Mikihisa , Satoh Shinobu , Kamada Hiroshi 
Published: December 2004

SummarySomatic embryogenesis is an obvious experimental evidence of totipotency, and is used as a model system for studying the mechanisms of de‐differentiation and re‐differentiation of plant cells. Although Arabidopsis is widely used as a model plant for genetic and molecular biological studies, there is no available tissue culture system for inducing somatic embryogenesis from somatic cells in this plant. We established a new tissue culture system using stress treatment to induce somatic embryogenesis in Arabidopsis. In this system, stress treatment induced formation of somatic embryos from shoot‐apical‐tip and floral‐bud explants. The somatic embryos grew into young plantlets with normal morphology, including cotyledons, hypocotyls, and roots, and some embryo‐specific genes (ABI3 and FUS3) were expressed in these embryos. Several stresses (osmotic, heavy metal ion, and dehydration stress) induced somatic embryogenesis, but the optimum stress treatment differed between different stressors. When we used mannitol to cause osmotic stress, the optimal conditions for somatic embryogenesis were 6–9 h of culture on solid B5 medium containing 0.7 m mannitol, after which the explants were transferred to B5 medium containing 2,4‐dichlorophenoxyacetic acid (2,4‐D, 4.5 µm), but no mannitol. Using this tissue culture system, we induced somatic embryogenesis in three major ecotypes of Arabidopsis thaliana– Ws, Col, and Ler.
Arabidopsis microarrays identify conserved and differentially expressed genes involved in shoot growth and development from distantly related plant species
Authors: Horvath David P. , Schaffer Robert , West Mark , Wisman Ellen 
Published: December 2004

SummaryExpressed sequence tags (EST)‐based microarrays are powerful tools for gene discovery and signal transduction studies in a small number of well‐characterized species. To explore the usefulness of this technique for poorly characterized species, we have hybridized the 11 522‐element Arabidopsis microarrays with labeled cDNAs from mature leaf and shoot apices from several different species. Expression of 23 to 47% of the genes on the array was detected, demonstrating that a large number of genes from distantly related species can be surveyed on Arabidopsis arrays. Differential expression of genes with known functions was indicative of the physiological state of the tissues tested. Genes involved in cell division, stress responses, and development were conserved and expressed preferentially in growing shoots.
Interaction between two mitogen‐activated protein kinases during tobacco defense signaling
Authors: Liu Yidong , Jin Hailing , Yang Kwang‐Yeol , Kim Cha Young , Baker Barbara , Zhang Shuqun 
Published: December 2004

SummaryPlant mitogen‐activated protein kinases (MAPKs) represented by tobacco wounding‐induced protein kinase (WIPK) have unique regulation at the level of transcription in response to stresses. By using transcriptional and translational inhibitors, it has been shown previously that WIPK gene expression and de novo protein synthesis are required for the high‐level activity of WIPK in cells treated with elicitins from Phytophthora spp. However, regulation of WIPK expression and the role(s) of WIPK in plant disease resistance are unknown. In this report, we demonstrate that WIPK gene transcription is regulated by phosphorylation and de‐phosphorylation events. Interestingly, salicylic acid‐induced protein kinase (SIPK) was identified as the kinase involved in regulating WIPK gene expression based on both gain‐of‐function and loss‐of‐function analyses. This finding revealed an additional level of interaction between SIPK and WIPK, which share an upstream MAPKK, NtMEK2. Depending on whether WIPK shares its downstream targets with SIPK, it could either function as a positive feed‐forward regulator of SIPK or initiate a new pathway. Consistent with the first scenario, co‐expression of WIPK with the active mutant of NtMEK2 leads to accelerated hypersensitive response (HR)‐like cell death in which SIPK also plays a role. Mutagenesis analysis revealed that the conserved common docking domain in WIPK is required for its function. Together with prior reports that (i) WIPK is activated in NN tobacco infected with tobacco mosaic virus, and (ii) PVX virus‐induced gene silencing of WIPK attenuated N gene‐mediated resistance, we concluded that WIPK plays a positive role in plant disease resistance, possibly through accelerating the pathogen‐induced HR cell death.
The Arabidopsis COG1 gene encodes a Dof domain transcription factor and negatively regulates phytochrome signaling
Authors: Park Don Ha , Lim Pyung Ok , Kim Jeong Sik , Cho Dae Shik , Hong Sung Hyun , Nam Hong Gil 
Published: December 2004

SummaryLight is a critical environmental factor that influences almost all developmental aspects of plants, including seed germination, seedling morphogenesis, and transition to reproductive growth. Plants have therefore developed an intricate network of mechanisms to perceive and process environmental light information. To further characterize the molecular basis of light‐signaling processes in plants, we screened an activation tagging pool of Arabidopsis for altered photoresponses. A dominant mutation, cog1‐D, attenuated various red (R) and far‐red (FR) light‐dependent photoresponses. The mutation was caused by overexpression of a gene encoding a member of the Dof family of transcription factors. The photoresponses in Arabidopsis were inversely correlated with the expression levels of COG1 mRNA. When the COG1 gene was overexpressed in transgenic plants, the plants exhibited hyposensitive responses to R and FR light in a manner inversely dependent on COG1 mRNA levels. On the other hand, transgenic lines expressing antisense COG1 were hypersensitive to R and FR light. Expression of the COG1 gene is light inducible and requires phytochrome A (phyA) for FR light‐induced expression and phytochrome B (phyB) for R light‐induced expression. Thus, the COG1 gene functions as a negative regulator in both the phyA‐ and phyB‐signaling pathways. We suggest that these phytochromes positively regulate the expression of COG1, a negative regulator, as a mechanism for fine tuning the light‐signaling pathway.
TETRASPORE encodes a kinesin required for male meiotic cytokinesis in Arabidopsis
Authors: Yang C‐Y. , Spielman M. , Coles J. P. , Li Y. , Ghelani S. , Bourdon V. , Brown R. C. , Lemmon B. E. , Scott R. J. , Dickinson H. G. 
Published: December 2004

SummaryA key step in pollen formation is the segregation of the products of male meiosis into a tetrad of microspores, each of which develops into a pollen grain. Separation of microspores does not occur in tetraspore (tes) mutants of Arabidopsis thaliana, owing to the failure of male meiotic cytokinesis. tes mutants thus generate large ‘tetraspores’ containing all the products of a single meiosis. Here, we report the positional cloning of the TES locus and details of the role played by the TES product in male cytokinesis. The predicted TES protein includes an N‐terminal domain homologous to kinesin motors and a C‐terminus with little similarity to other proteins except for a small number of plant kinesins. These include the Arabidopsis HINKEL protein and NACK1 and two from tobacco (), which are involved in microtubule organization during mitotic cytokinesis. Immunocytochemistry shows that the characteristic radial arrays of microtubules associated with male meiotic cytokinesis fail to form in tes mutants. The TES protein therefore is likely to function as a microtubule‐associated motor, playing a part either in the formation of the radial arrays that establish spore domains following meiosis, or in maintaining their stability.
Repression of gene expression by Arabidopsis HD2 histone deacetylases
Authors: Wu Keqiang , Tian Lining , Zhou Changhe , Brown Daniel , Miki Brian 
Published: December 2004

SummaryThe four HD2 proteins of Arabidopsis thaliana (AtHD2A–D) belong to a unique class of histone deacetylases that is plant specific. Previously, we have demonstrated that one of the members, AtHD2A, can mediate transcriptional repression when targeted to the promoter of a reporter gene. Here, we report that AtHD2B and AtHD2C can also repress gene expression. AtHD2A and AtHD2C differ from AtHD2B and AtHD2D in the composition of their structural domains. Our data show that both structural types play a role in the repression of gene transcription. We demonstrate that AtHD2A can mediate gene repression through interactions with transcription factors in plants. By fusing AtHD2A with the DNA‐binding domain of the plant transcriptional factor Pti4, the expression of a GCC box containing reporter gene was repressed. We also demonstrated repression of a GUS gene with GAL4 enhancers using transgenic plants that expressed a GAL4/AtHD2A fusion gene. Furthermore, the expression of the GAL4/AtHD2A protein using the seed‐specific napin promoter (NAP2) and the constitutive tCUP promoter demonstrated that repression of transgenes could be achieved in a tissue‐specific or unrestricted manner. Targeting of HD2 proteins to specific promoters using transcription factor DNA‐binding domains may therefore provide a new technology for silencing target genes and pathways in plants as well as for assessing the function of unknown transcription factors.
Reactive electrophile species activate defense gene expression in Arabidopsis
Authors: Alméras Emmanuelle , Stolz Stéphanie , Vollenweider Sabine , Reymond Philippe , Mène‐Saffrané Laurent , Farmer Edward E. 
Published: December 2004

SummaryCompounds containing α,β‐unsaturated carbonyl groups are increasingly implicated as potent regulators of gene expression; some are powerful cytotoxins known to accumulate at the site of lesion formation in host–pathogen interactions. We used a robust measurement of photosynthetic efficiency to quantify the toxicity of a variety of lipid derivatives in Arabidopsis leaves. Small α,β‐unsaturated carbonyl compounds (e.g. acrolein and methyl vinyl ketone) were highly active and proved to be potent stimulators of expression of the pathogenesis‐related gene HEL (PR4). These small volatile electrophiles were far more active than larger alkenal homologs like 2(E)‐hexenal, and activated HEL expression in a manner independent of salicylate, ethylene, and jasmonate production/perception. Electrophile treatment massively increased the levels of unesterified cyclopentenone jasmonates, which themselves are electrophiles. Patterns of gene expression in response to electrophile treatment and in response to avirulent bacteria were compared, which revealed strikingly similar transcript profiles. The results broaden the range of known biologic effects of reactive electrophile species to include the activation of a pathogenesis‐related gene (HEL) and genes involved in metabolism. Electrophiles can act as mediators of both genetic and biochemical effects on core defense signal transduction.
Signaling activities among the Arabidopsis phyB/D/E‐type phytochromes: a major role for the central region of the apoprotein
Authors: Sharrock Robert A. , Clack Ted , Goosey Lynn 
Published: December 2004

SummaryThe Arabidopsis phyB, phyD, and phyE phytochromes regulate plant developmental and growth responses to continuous red light (R) and to the ratio of R to far‐red (FR) light. The activities of these three photoreceptors in the control of seedling growth have been compared using a transgenic assay based upon induction of R‐hypersensitivity of hypocotyl elongation by overexpression of the apoproteins from the 35S promoter. 35S‐phyB, 35S‐phyD, and 35S‐phyE lines expressing similar levels of the respective phytochromes were isolated. Under pulses of R, phyB is very active in inducing a dwarf hypocotyl phenotype, whereas phyD and phyE are inactive. Under high‐fluence continuous R, phyD shows a gain in activity whereas phyE does not. These results demonstrate significant differences in the inherent regulatory activities of these receptor apoproteins. To localize the sequence determinants of these functional differences, chimeric proteins were constructed by shuffling amino‐terminal, central, and carboxy‐terminal regions of phyB and phyD. Overexpression analysis of the phyB/D chimeras shows that it is the central region of these proteins that is most critical in determining their respective activities.
Reduced cellulose synthesis invokes lignification and defense responses in Arabidopsis thaliana
Authors: Caño‐Delgado Ana , Penfield Steven , Smith Caroline , Catley Merryn , Bevan Michael 
Published: December 2004

SummaryThe cell wall determines the shape of plant cells and is also the primary interface for pathogen interactions. The structure of the cell wall can be modified in response to developmental and environmental cues, for example to strengthen the wall and to create barriers to pathogen ingress. The ectopic lignin 1‐1 and 1‐2 (eli1‐1 and eli1‐2) mutations lead to an aberrant deposition of lignin, a complex phenylpropanoid polymer. We show that the eli1 mutants occur in the cellulose synthase gene CESA3 in Arabidopsis thaliana and cause reduced cellulose synthesis, providing further evidence for the function of multiple CESA subunits in cellulose synthesis. We show that reduced levels of cellulose synthesis, caused by mutations in cellulose synthase genes and in genes affecting cell expansion, activate lignin synthesis and defense responses through jasmonate and ethylene and other signaling pathways. These observations suggest that mechanisms monitoring cell wall integrity can activate lignification and defense responses.
Ethylene‐mediated enhancement of apical hook formation in etiolated Arabidopsis thaliana seedlings is gibberellin dependent
Authors: Vriezen Wim H. , Achard Patrick , Harberd Nicholas P. , Van Der Straeten Dominique 
Published: December 2004

SummaryDark‐grown Arabidopsis seedlings develop an apical hook by differential elongation and division of hypocotyl cells. This allows the curved hypocotyl to gently drag the apex, which is protected by the cotyledons, upwards through the soil. Several plant hormones are known to be involved in hook development, including ethylene, which causes exaggeration of the hook. We show that gibberellins (GAs) are also involved in this process. Inhibition of GA biosynthesis with paclobutrazol (PAC) prevented hook formation in wild‐type (WT) seedlings and in constitutive ethylene response (ctr)1‐1, a mutant that exhibits a constitutive ethylene response. In addition, a GA‐deficient mutant (ga1‐3) did not form an apical hook in the presence of the ethylene precursor 1‐aminocyclopropane‐1‐carboxylate (ACC). Analysis of transgenic Arabidopsis seedlings expressing a green fluorescent protein (GFP)–repressor of ga1‐3 (RGA) fusion protein suggested that ACC inhibits cell elongation in the apical hook by inhibition of GA signaling. A decreased feedback of GA possibly causes an induction of GA biosynthesis based upon the expression of genes encoding copalyl diphosphate synthase (CPS; GA1) and GA 2‐oxidase (AtGA2ox1). Furthermore, expression of GASA1, a GA‐response gene, suggests that differential cell elongation in the apical hook might be a result of differential GA‐sensitivity.
Xa26, a gene conferring resistance to Xanthomonas oryzae pv. oryzae in rice, encodes an LRR receptor kinase‐like protein
Authors: Sun Xinli , Cao Yinglong , Yang Zhifen , Xu Caiguo , Li Xianghua , Wang Shiping , Zhang Qifa 
Published: December 2004

SummaryRice bacterial blight, caused by Xanthomonas oryzae pv. oryzae (Xoo), is one of the most serious rice diseases worldwide. A rice gene, Xa26, conferring resistance against Xoo at both seedling and adult stages was isolated by map‐based cloning strategies from the rice cultivar Minghui 63. Xa26 belongs to a multigene family consisting of four members. It encodes a leucine‐rich repeat (LRR) receptor kinase‐like protein and is constitutively expressed. Sequence analysis revealed that IRBB3 and Zhachanglong lines that are resistant to a broad range of Xoo strains, also carry Xa26. However, significant difference in lesion length was observed among these lines after inoculation with a set of Xoo strains. Moreover, transgenic plants carrying Xa26 showed enhanced resistance compared with the donor line of the gene in both seedling and adult stages. These results suggest that the resistance conferred by Xa26 is influenced by the genetic background.
Identification of Pseudomonas syringae type III effectors that can suppress programmed cell death in plants and yeast
Authors: Jamir Yashitola , Guo Ming , Oh Hye‐Sook , Petnicki‐Ocwieja Tanja , Chen Shaorong , Tang Xiaoyang , Dickman Martin B. , Collmer Alan , R. Alfano James 
Published: December 2004

SummaryThe Pseudomonas syringae pv. tomato DC3000 type III secretion system (TTSS) is required for bacterial pathogenicity on plants and elicitation of the hypersensitive response (HR), a programmed cell death (PCD) that occurs on resistant plants. Cosmid pHIR11 enables non‐pathogens to elicit an HR dependent upon the TTSS and the effector HopPsyA. We used pHIR11 to determine that effectors HopPtoE, avirulence AvrPphEPto, AvrPpiB1Pto, AvrPtoB, and HopPtoF could suppress a HopPsyA‐dependent HR on tobacco and Arabidopsis. Mixed inoculum and Agrobacterium‐mediated transient expression experiments confirmed that suppressor action occurred within plant cells. These suppressors, with the exception of AvrPpiB1Pto, inhibited the expression of the tobacco pathogenesis‐related (PR) gene PR1a. DC3000 suppressor mutants elicited an enhanced HR consistent with these mutants lacking an HR suppressor. Additionally, HopPtoG was identified as a suppressor on the basis of an enhanced HR produced by a hopPtoG mutant. Remarkably, these proteins functioned to inhibit the ability of the pro‐apoptotic protein, Bax to induce PCD in plants and yeast, indicating that these effectors function as anti‐PCD proteins in a trans‐kingdom manner. The high proportion of effectors that suppress PCD suggests that suppressing plant immunity is one of the primary roles for DC3000 effectors and a central requirement for P. syringae pathogenesis.