bluuebunny/crossref_metadata_2025_split huggingface dataset:
ABA depolarizes guard cells in intact plants, through a transient activation of R‐ and S‐type anion channels
Authors: Roelfsema M. Rob G. , Levchenko Victor , Hedrich Rainer 
Published: December 2004

SummaryDuring drought, the plant hormone abscisic acid (ABA) induces rapid stomatal closure and in turn reduces transpiration. Stomatal closure is accompanied by large ion fluxes across the plasma membrane, carried by K+ and anion channels. We recorded changes in the activity of these channels induced by ABA, for guard cells of intact Vicia faba plants. Guard cells in their natural environment were impaled with double‐barrelled electrodes, and ABA was applied via the leaf surface. In 45 out of 85 cells tested, ABA triggered a transient depolarization of the plasma membrane. In these cells, the membrane potential partially recovered in the presence of ABA; however, a full recovery of the membrane potentials was only observed after removal of ABA. Repetitive ABA responses could be evoked in single cells, but the magnitude of the response varied from one hormone application to the other. The transient depolarization correlated with the activation of anion channels, which peaked 5 min after introduction of the stimulus. In guard cells with a moderate increase in plasma membrane conductance (ΔG < 5 nS), ABA predominantly activated voltage‐independent (slow (S)‐type) anion channels. During strong responses (ΔG > 5 nS), however, ABA activated voltage‐dependent (rapid (R)‐type) in addition to S‐type anion channels. We conclude that the combined activation of these two channel types leads to the transient depolarization of guard cells. The nature of this ABA response correlates with the transient extrusion of Cl− from guard cells and a rapid but confined reduction in stomatal aperture.
Activation of a COI1‐dependent pathway in Arabidopsis by Pseudomonas syringae type III effectors and coronatine
Authors: He Ping , Chintamanani Satya , Chen Zhongying , Zhu Lihuang , Kunkel Barbara N. , Alfano James R. , Tang Xiaoyan , Zhou Jian‐Min 
Published: December 2004

SummaryGram‐negative bacteria use a variety of virulence factors including phytotoxins, exopolysaccharides, effectors secreted by the type III secretion system, and cell‐wall‐degrading enzymes to promote parasitism in plants. However, little is known about how these virulence factors alter plant cellular responses to promote disease. In this study, we show that virulent Pseudomonas syringae strains activate the transcription of an Arabidopsis ethylene response factor (ERF) gene, RAP2.6, in a coronatine insensitive 1 (COI1)‐dependent manner. A highly sensitive RAP2.6 promoter‐firefly luciferase (RAP2.6‐LUC) reporter line was developed to monitor activities of various bacterial virulence genes. Analyses of P. syringae pv. tomato DC3000 mutants indicated that both type III secretion system and the phytotoxin coronatine are required for RAP2.6 induction. We show that at least five individual type III effectors, avirulence B (AvrB), AvrRpt2, AvrPphB, HopPtoK, and AvrPphEPto, contributed to RAP2.6 induction. Gene‐for‐gene recognition was not involved in RAP2.6 induction because plants lacking RPM1 and RPS2 responded normally to AvrB and AvrRpt2 in RAP2.6 expression. Interestingly, the role of coronatine in RAP2.6 induction can be partially substituted by the addition of avrB in DC3000, suggesting that AvrB may mimic coronatine. These results suggest that P. syringae type III effectors and coronatine act by augmenting a COI1‐dependent pathway to promote parasitism.
Functional analyses of the flowering time geneOsMADS50, the putativeSUPPRESSOR OF OVEREXPRESSION OF CO 1/AGAMOUS‐LIKE 20(SOC1/AGL20) ortholog in rice
Authors: Lee Shinyoung , Kim Joonyul , Han Jong‐Jin , Han Min‐Jung , An Gynheung 
Published: December 2004

SummaryA late‐flowering mutant was isolated from rice T‐DNA‐tagging lines. T‐DNA had been integrated into the K‐box region ofOryza sativa MADS50(OsMADS50), which shares 50.6% amino acid identity with theArabidopsisMADS‐box geneSUPPRESSOR OF OVEREXPRESSION OF CO 1/AGAMOUS‐LIKE 20(SOC1/AGL20). While overexpression ofOsMADS50caused extremely early flowering at the callus stage,OsMADS50RNAi plants exhibited phenotypes of late flowering and an increase in the number of elongated internodes. This confirmed that the phenotypes observed in the knockout (KO) plants are because of the mutation inOsMADS50. RT‐PCR analyses of theOsMADS50KO and ubiquitin (ubi):OsMADS50plants showed thatOsMADS50is an upstream regulator ofOsMADS1,OsMADS14,OsMADS15,OsMADS18, andHd (Heading date)3a, but works either parallel with or downstream ofHd1andO. sativa GIGANTEA(OsGI). These results suggest thatOsMADS50is an important flowering activator that controls various floral regulators in rice.
Expression and function of HD2‐type histone deacetylases in Arabidopsis development
Authors: Zhou Changhe , Labbe Helene , Sridha Sunandini , Wang Li , Tian Lining , Latoszek‐Green Marysia , Yang Zhen , Brown Daniel , Miki Brian , Wu Keqiang 
Published: December 2004

SummaryHD2 (histone deacetylase) proteins are plant‐specific histone deacetylases (HDACs). The Arabidopsis genome contains four HD2 genes, namely HD2A, HD2B, HD2C, and HD2D. We have previously demonstrated that HD2A, HD2B, and HD2C can repress transcription directly by targeting to promoters in planta. Here, we show that the N‐terminal conserved motif (EFWG) and histidine 25 (H25), a potential catalytic residue, were important for the gene repression activity of HD2A. In situ hybridization indicated that HD2A, HD2B, and HD2C were expressed in ovules, embryos, shoot apical meristems, and primary leaves. Furthermore, all three genes were strongly induced during the process of somatic embryogenesis. HD2D mRNA was only detected in the stems and flowers with young siliques and may have adopted different functions. Using green fluorescent protein (GFP) fusions, we demonstrated that HD2A, HD2B, and HD2C accumulated in the nuclei of Arabidopsis cells. Overexpression of 35S::GFP–HD2A in transgenic Arabidopsis plants generated pleiotropic developmental abnormalities, including abnormal leaves, delayed flowering, and aborted seed development. The data showed that normal pattern of HD2 expression was essential for normal plant development and that HD2A, HD2B, and HD2C may be needed for embryogenesis and embryo development. Reverse transcriptase (RT)‐PCR analysis revealed that a number of genes involved in seed development and maturation were repressed in the 35S::GFP–HD2A plants, supporting a role of HD2A in the regulation of gene expression during seed development.
Expression profiling of phyB mutant demonstrates substantial contribution of other phytochromes to red‐light‐regulated gene expression during seedling de‐etiolation
Authors: Tepperman James M. , Hudson Matthew E. , Khanna Rajnish , Zhu Tong , Chang Sherman H. , Wang Xun , Quail Peter H. 
Published: December 2004

SummaryDifferent Arabidopsis phytochrome (phy) family members (phyA through phyE) display differential photosensory and/or physiological functions in regulating growth and developmental responses to light signals. To identify the genes regulated by phyB in response to continuous monochromatic red light (Rc) during the induction of seedling de‐etiolation, we have performed time‐course, microarray‐based expression profiling of wild type (WT) and phyB null mutants. Comparison of the observed expression patterns with those induced by continuous monochromatic far‐red light (FRc; perceived exclusively by phyA) in WT and phyA null‐mutant seedlings suggests early convergence of the FRc and Rc photosensory pathways to control a largely common transcriptional network. phyB mutant seedlings retain a surprisingly high level of responsiveness to Rc for the majority of Rc‐regulated genes on the microarray, indicating that one or more other phys have a major role in regulating their expression. Combined with the robust visible morphogenic phenotype of the phyB mutant in Rc, these data suggest that different members of the phy family act in organ‐specific fashion in regulating seedling de‐etiolation. Specifically, phyB appears to be the dominant, if not exclusive, photoreceptor in regulating a minority population of genes involved in suppression of hypocotyl cell elongation in response to Rc signals. By contrast, this sensory function is apparently shared by one or more other phys in regulating the majority Rc‐responsive gene set involved in other important facets of the de‐etiolation process in the apical region, such as cotyledon cell expansion.
Drought tolerance established by enhanced expression of the CC–NBS–LRR gene, ADR1, requires salicylic acid, EDS1 and ABI1
Authors: Chini Andrea , Grant John J. , Seki Motoaki , Shinozaki Kazuo , Loake Gary J. 
Published: December 2004

SummaryAn activation‐tagged allele of activated disease resistance 1 (ADR1) has previously been shown to convey broad spectrum disease resistance. ADR1 was found to encode a coiled‐coil (CC)–nucleotide‐binding site (NBS)–leucine‐rich repeat (LRR) protein, which possessed domains of homology with serine/threonine protein kinases. Here, we show that either constitutive or conditional enhanced expression of ADR1 conferred significant drought tolerance. This was not a general feature of defence‐related mutants because cir (constitutive induced resistance)1, cir2 and cpr (constitutive expressor of PR genes)1, which constitutively express systemic acquired resistance (SAR), failed to exhibit this phenotype. Cross‐tolerance was not a characteristic of adr1 plants, rather they showed increased sensitivity to thermal and salinity stress. Hence, adr1‐activated signalling may antagonise some stress responses. Northern analysis of abiotic marker genes revealed that dehydration‐responsive element (DRE)B2A but not DREB1A, RD (response to dehydration)29A or RD22 was expressed in adr1 plant lines. Furthermore, DREB2A expression was salicylic acid (SA) dependent but NPR (non‐expressor of PR genes)1 independent. In adr1/ADR1 nahG (naphthalene hydroxylase G), adr1/ADR1 eds (enhanced disease susceptibility)1 and adr1/ADR1 abi1 double mutants, drought tolerance was significantly reduced. Microarray analyses of plants containing a conditional adr1 allele demonstrated that a significant number of the upregulated genes had been previously implicated in responses to dehydration. Therefore, biotic and abiotic signalling pathways may share multiple nodes and their outputs may have significant functional overlap.
Light induces phenylpropanoid metabolism in Arabidopsis roots
Authors: Hemm Matthew R. , Rider Stanley D. , Ogas Joseph , Murry Daryl J. , Chapple Clint 
Published: December 2004

SummaryExperiments have shown that many phenylpropanoid genes are highly expressed in light‐grown Arabidopsis roots. Studies employing reporter gene constructs have indicated that the expression of these genes is localized not only to the lignifying root vasculature, but also to non‐lignifying tissues, such as the root cortex, suggesting that the proteins encoded by these genes may be involved in aspects of phenylpropanoid metabolism other than lignification. Consistent with this hypothesis, roots of etiolated and soil‐grown plants contain almost no soluble phenylpropanoids, but exposure to light leads to the accumulation of flavonoids, as well as high levels of coniferin and syringin (coniferyl and sinapyl‐4‐O‐glycosides), compounds not previously reported to be accumulated in Arabidopsis. To elucidate the mechanism by which light induces root secondary metabolism, extracts of mutants defective in light perception and light responses were analyzed for phenylpropanoid content. The results of these assays showed that phytochrome (PHY)B and cryptochrome (CRY)2 are the primary photoreceptors involved in light‐dependent phenylpropanoid accumulation, and that the hypocotyl elongated (HY5) transcription factor is also required for this response. The presence of phenylpropanoids in etiolated roots of cop (constitutively photomorphogenic)1, cop9, and det (de‐etiolated)1 mutants indicate that the corresponding wild‐type genes are required to repress root phenylpropanoid biosynthesis in the absence of light. Biochemical analysis of root cell walls and analysis of phenylpropanoid gene expression suggest that coniferin and syringin accumulation may be the result of both increased biosynthesis and decreased conversion of these compounds into other phenylpropanoid end products. Finally, our data suggest that the accumulation of coniferin, syringin, and flavonoids in Arabidopsis roots is a high‐irradiance response (HIR), and suggest that comparative analysis of light‐ and dark‐grown Arabidopsis roots may provide new insights into both phenylpropanoid biosynthesis and light signaling in plants.
An intragenic tandem duplication in a transcriptional regulatory gene for anthocyanin biosynthesis confers pale‐colored flowers and seeds with fine spots in Ipomoea tricolor
Authors: Park Kyeung‐Il , Choi Jeong‐Doo , Hoshino Atsushi , Morita Yasumasa , Iida Shigeru 
Published: December 2004

SummaryWhile the wild‐type morning glory (Ipomoea tricolor) displays bright‐blue flowers and dark‐brown seeds, its spontaneous mutant, Blue Star, carrying the mutable ivory seed‐variegated (ivs‐v) allele, exhibits pale‐blue flowers with a few fine blue spots and ivory seeds with tiny dark‐brown spots. The mutable allele is caused by an intragenic tandem duplication of 3.3 kbp within a gene for transcriptional activator containing a basic helix‐loop‐helix (bHLH) DNA‐binding motif. Each of the tandem repeats is flanked by a 3‐bp sequence AAT, indicating that the 3‐bp microhomology is used to generate the tandem duplication. The transcripts in the pale‐blue flower buds of the mutant contain an internal 583‐bp tandem duplication that results in the production of a truncated polypeptide lacking the bHLH domain. The mRNA accumulation of most of the structural genes encoding enzymes for anthocyanin biosynthesis in the flower buds of the mutant was significantly reduced. The transcripts identical to the wild‐type mRNAs for the transcriptional activator were present abundantly in blue spots of the variegated flowers, whereas the transcripts containing the 583‐bp tandem duplication were predominant in the pale‐blue background of the same flowers. The flower and seed variegations studied here are likely to be caused by somatic homologous recombination between an intragenic tandem duplication in the gene encoding a bHLH transcriptional activator for anthocyanin biosynthesis, whereas various flower variegations are reported to be caused by excision of DNA transposons inserted into pigmentation genes.
Detection of protein–protein interactions in plants using bimolecular fluorescence complementation
Authors: Bracha‐Drori Keren , Shichrur Keren , Katz Aviva , Oliva Moran , Angelovici Ruthie , Yalovsky Shaul , Ohad Nir 
Published: December 2004

SummaryProtein function is often mediated via formation of stable or transient complexes. Here we report the determination of protein–protein interactions in plants using bimolecular fluorescence complementation (BiFC). The yellow fluorescent protein (YFP) was split into two non‐overlapping N‐terminal (YN) and C‐terminal (YC) fragments. Each fragment was cloned in‐frame to a gene of interest, enabling expression of fusion proteins. To demonstrate the feasibility of BiFC in plants, two pairs of interacting proteins were utilized: (i) the α and β subunits of the Arabidopsis protein farnesyltransferase (PFT), and (ii) the polycomb proteins, FERTILIZATION‐INDEPENDENT ENDOSPERM (FIE) and MEDEA (MEA). Members of each protein pair were transiently co‐expressed in leaf epidermal cells of Nicotiana benthamiana or Arabidopsis. Reconstitution of a fluorescing YFP chromophore occurred only when the inquest proteins interacted. No fluorescence was detected following co‐expression of free non‐fused YN and YC or non‐interacting protein pairs. Yellow fluorescence was detected in the cytoplasm of cells that expressed PFT α and β subunits, or in nuclei and cytoplasm of cells that expressed FIE and MEA. In vivo measurements of fluorescence spectra emitted from reconstituted YFPs were identical to that of a non‐split YFP, confirming reconstitution of the chromophore. Expression of the inquest proteins was verified by immunoblot analysis using monoclonal antibodies directed against tags within the hybrid proteins. In addition, protein interactions were confirmed by immunoprecipitations. These results demonstrate that plant BiFC is a simple, reliable and relatively fast method for determining protein–protein interactions in plants.
The BOS loci of Arabidopsis are required for resistance to Botrytis cinerea infection
Authors: Veronese Paola , Chen Xi , Bluhm Burton , Salmeron John , Dietrich Robert , Mengiste Tesfaye 
Published: December 2004

SummaryThree Botrytis‐susceptible mutants bos2, bos3, and bos4 which define independent and novel genetic loci required for Arabidopsis resistance to Botrytis cinerea were isolated. The bos2 mutant is susceptible to B. cinerea but retains wild‐type levels of resistance to other pathogens tested, indicative of a defect in a response pathway more specific to B. cinerea. The bos3 and bos4 mutants also show increased susceptibility to Alternaria brassicicola, another necrotrophic pathogen, suggesting a broader role for these loci in resistance. bos4 shows the broadest range of effects on resistance, being more susceptible to avirulent strain of Pseudomonas syringae pv. tomato. Interestingly, bos3 is more resistant than wild‐type plants to virulent strains of the biotrophic pathogen Peronospora parasitica and the bacterial pathogen P. syringae pv. tomato. The Pathogenesis Related gene 1 (PR‐1), a molecular marker of the salicylic acid (SA)‐dependent resistance pathway, shows a wild‐type pattern of expression in bos2, while in bos3 this gene was expressed at elevated levels, both constitutively and in response to pathogen challenge. In bos4 plants, PR‐1 expression was reduced compared with wild type in response to B. cinerea and SA. In bos3, the mutant most susceptible to B. cinerea and with the highest expression of PR‐1, removal of SA resulted in reduced PR‐1 expression but no change to the B. cinerea response. Expression of the plant defensin gene PDF1‐2 was generally lower in bos mutants compared with wild‐type plants, with a particularly strong reduction in bos3. Production of the phytoalexin camalexin is another well‐characterized plant defense response. The bos2 and bos4 mutants accumulate reduced levels of camalexin whereas bos3 accumulates significantly higher levels of camalexin than wild‐type plants in response to B. cinerea. The BOS2, BOS3, and BOS4 loci may affect camalexin levels and responsiveness to ethylene and jasmonate. The three new mutants appear to mediate disease responses through mechanisms independent of the previously described BOS1 gene. Based on the differences in the phenotypes of the bos mutants, it appears that they affect different points in defense response pathways.
Virus‐induced gene silencing as a tool for functional genomics in a legume species
Authors: Constantin Gabriela D. , Krath Britta N. , MacFarlane Stuart A. , Nicolaisen Mogens , Elisabeth Johansen Ida , Lund Ole S. 
Published: December 2004

SummaryVirus‐induced gene silencing (VIGS) is an attractive reverse‐genetics tool for studies of gene function. However, efficient VIGS has only been accomplished in a few plant species. In order to extend the application of VIGS, we examined whether a VIGS vector based on Pea early browning virus (PEBV) would produce recognizable phenotypes in Pisum sativum. A plasmid vector of PEBV was modified to allow agro‐inoculation and insertion of heterologous sequences. cDNA fragments of the P. sativum phytoene desaturase (PDS), LEAFY (LFY) and KORRIGAN1 (KOR1) homologues were inserted into the PEBV RNA2 vector, replacing the genes required for nematode transmission. Pisum sativum inoculated with PEBV carrying a fragment of PsPDS developed characteristic photo‐bleached leaves and this phenotype was associated with a significant reduction in PsPDS mRNA. The P. sativum homologue of LFY is known as UNIFOLIATA (UNI). Plants inoculated with PEBV carrying a fragment of UNI developed distorted flowers and leaves with modified architecture, which are also observed in UNI‐mutants. In Arabidopsis thaliana, the KOR1‐mutant is characterized by an extreme dwarf phenotype. Pisum sativum plants inoculated with PEBV carrying a fragment of PsKOR1 displayed a significant reduction in height and inhibition of root growth. The PEBV VIGS vector did not affect the ability of P. sativum to flower, set seeds, and form nodules characteristic of symbiosis with rhizobium. These results suggest that the PEBV vector can be applied to functional genomics in a legume species to study genes involved in a wide range of biological processes.
The mitochondrion – an organelle commonly involved in programmed cell death in Arabidopsis thaliana
Authors: Yao Nan , Eisfelder Bartholomew J. , Marvin James , Greenberg Jean T. 
Published: December 2004

SummaryPlant cells undergoing programmed cell death (PCD) at late stages typically show chromatin condensation and endonucleolytic cleavage prior to obvious membrane or organelle ultrastructural changes. To investigate possible early PCD‐associated events, we used microscopic observations and flow cytometry to quantitate mitochondrial membrane potential (ΔΨm) changes during PCD at the single cell and population levels using Arabidopsis protoplasts. A ΔΨm loss was commonly induced early during plant PCD and was important for PCD execution, as evidenced by the concomitant reduction of the change in ΔΨm and PCD by cyclosporin A, which inhibits mitochondrial permeability transition pores in animal cells. ΔΨm loss occurred prior to nuclear morphological changes and was only associated with mitochondrial cytochrome c release (an apoptotic trigger in animals) in response to one of three PCD elicitors. Three different stimuli in wild type implicated ΔΨm changes in PCD: ceramide, protoporphyrin IX, and the hypersensitive response elicitor AvrRpt2. Additionally, the behavior of the conditional ectopic cell death mutant accelerated cell death2 and ACD2‐overproducing plants also implicated ΔΨm alteration as key for PCD execution. Because ACD2 is largely a chloroplast component in mature plants, the observation that the cell death in acd2 mutants requires changes in mitochondrial functions implicates communication between chloroplasts and mitochondria in mediating PCD activation. We suggest that ΔΨm loss is a common early marker in plant PCD, similar to what has been documented in animals. However, unlike in animal cells, in plant cells, mitochondrial cytochrome c release is not an obligatory step in PCD control.