Arabidopsis
not annotated - annotated - LINNAEUS only
20807372
Increased intracellular H2O2 availability preferentially drives glutathione accumulation in vacuoles and chloroplasts.
One biochemical response to increased H2O2 availability is the accumulation of glutathione disulphide (GSSG), the disulphide form of the key redox buffer glutathione. It remains unclear how this potentially important oxidative stress response impacts on the different sub-cellular glutathione pools. We addressed this question by using two independent in situ glutathione labelling techniques in Arabidopsis wild type (Col-0) and the GSSG-accumulating cat2 mutant. A comparison of in situ labelling with monochlorobimane (MCB) and in vitro labelling with monobromobimane (MBB) revealed that, whereas in situ labelling of Col-0 leaf glutathione was complete within 2 h incubation, about 50% of leaf glutathione remained inaccessible to MCB in cat2. High-performance liquid chromatography (HPLC) and enzymatic assays showed that this correlated tightly with the glutathione redox state, pointing to significant in vivo pools of GSSG in cat2 that were unavailable for MCB labelling. Immunogold labelling of leaf sections to estimate sub-cellular glutathione distribution showed that the accumulated GSSG in cat2 was associated with only a minor increase in cytosolic glutathione but with a 3- and 10-fold increase in plastid and vacuolar pools, respectively. The data are used to estimate compartment-specific glutathione concentrations under optimal and oxidative stress conditions, and the implications for redox homeostasis and signalling are discussed.
20854394
SGT1 contributes to coronatine signaling and Pseudomonas syringae pv. tomato disease symptom development in tomato and Arabidopsis.
* Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) causes an economically important bacterial speck disease on tomato and produces symptoms with necrotic lesions surrounded by chlorosis. The chlorosis is mainly attributed to a jasmonic acid (JA)-isoleucine analogue, coronatine (COR), produced by Pst DC3000. However, the molecular processes underlying lesion development and COR-induced chlorosis are poorly understood. * In this study, we took advantage of a chlorotic phenotype elicited by COR on Nicotiana benthamiana leaves and virus-induced gene silencing (VIGS) as a rapid reverse genetic screening tool and identified a role for SGT1 (suppressor of G2 allele of skp1) in COR-induced chlorosis. * Silencing of SGT1 in tomato resulted in reduction of disease-associated symptoms (cell death and chlorosis), suggesting a molecular connection between COR-induced chlorosis and cell death. In Arabidopsis, AtSGT1b but not AtSGT1a was required for COR responses, including root growth inhibition and Pst DC3000 symptom (water soaked lesion) development. Notably, overexpression of AtSGT1b did not alter Pst DC3000 symptoms or sensitivity to COR. * Taken together, our results demonstrate that SGT1/SGT1b is required for COR-induced chlorosis and subsequent necrotic disease development in tomato and Arabidopsis. SGT1 is therefore a component of the COR/JA-mediated signal transduction pathway.
20880224
Arabidopsis thaliana populations show clinal variation in a climatic gradient associated with altitude.
* Understanding the adaptive basis of life history variation is a central goal in evolutionary ecology. The use of model species enables the combination of molecular mechanistic knowledge with ecological and evolutionary questions, but the study of life history variation in natural environments is required to merge these disciplines. * Here, we tested for clinal variation in life history and associated traits along an environmental and altitudinal gradient in the model species Arabidopsis thaliana. Seventeen natural populations of A. thaliana were geo-referenced in north-eastern Spain on a gradient in which precipitation increases but maximum spring temperature and minimum winter temperature decrease with altitude. * One hundred and eighty-nine genotypes from the 17 populations were grown under uniform controlled conditions. Variations in traits related to biomass allocation, fecundity, phenology and vegetative growth were tested for relationships with the altitude and climatic variables associated with the home sites. Above-ground mass, number of rosette leaves at bolting, developmental time and seed weight increased with the home site's altitude. Root allocation, vegetative growth during winter and number of seeds decreased with altitude. * We suggest that the differences among home sites provide clues to the variation in adaptive strategies associated with the climatic gradient. We compared these results with adaptations and clinal relationships reported for other species and with molecular mechanisms described in Arabidopsis.
20946418
A seed high-lysine trait is negatively associated with the TCA cycle and slows down Arabidopsis seed germination.
* Lysine is a nutritionally important essential amino acid, but significant elevation of its levels in Arabidopsis seeds, by enhancing its synthesis and blocking its catabolism, causes a retardation of germination. Here, we hypothesized that this negative effect is associated with changes in primary metabolism and gene expression programs that are essential for early germination. * Seeds at different stages of germination sensu stricto of the seed-high-lysine genotype were subjected to detailed analysis of primary metabolism, using GC-MS, as well as microarray analysis and two-dimensional, isoelectric focusing, sodium dodecylsulfate polyacrylamide gel electrophoresis, to detect storage protein mobilization. * Our results exposed a major negative effect of the seed-specific increased lysine synthesis and knockout of its catabolism on the levels of a number of TCA cycle metabolites. This metabolic alteration also influences significantly the transcriptome, primarily attenuating the boost of specific transcriptional programs that are essential for seedling establishment, such as the onset of photosynthesis, as well as the turnover of specific transcriptional programs associated with seed embryonic traits. * Our results indicate that catabolism of the aspartic acid family of amino acids is an important contributor to the energy status of plants, and hence to the onset of autotrophic growth-associated processes during germination.
20955225
Auxin depletion in barley plants under high-temperature conditions represses DNA proliferation in organelles and nuclei via transcriptional alterations.
Many plant species are susceptible to high-temperature (HT) injury during reproductive development. We recently demonstrated that HT represses the expression of YUCCA auxin biosynthesis genes and reduces endogenous auxin in the developing anthers of barley and Arabidopsis. Here, we show that DNA proliferation in mitochondria, chloroplasts and nuclei of developing panicles is inhibited with increasing temperatures in barley. Following DNA proliferation suppression, terminal abnormalities were observed in the organelles of anther wall cells, including mitochondrial swelling and overdevelopment of chloroplasts. Comprehensive transcriptome analyses using both reproductive organs and vegetative tissues showed high and positive pairwise correlations between the expression profiles of auxin-induced genes, DNA replication-related genes and mitochondrial-related genes. In contrast, the expression profiles of auxin-repressed protein genes and photosynthesis-/chloroplast-related genes were negatively correlated with those of the previously mentioned genes. Under HT conditions, the former was repressed and the latter was up-regulated in the developing panicles. Furthermore, application of exogenous auxin promoted the expression of DNA replication-related genes under HT conditions, inducing anther cell proliferation. These suggest that compromised auxin biosynthesis/IAA level under HT condition results in nuclear and organellar DNA proliferation arrest due to co-transcriptional alterations.
21039560
The second face of a known player: Arabidopsis silencing suppressor AtXRN4 acts organ-specifically.
Plant viruses exploit the symplastic transport pathway provided by plasmodesmata by encoding for specialized movement proteins, which interact with host factors to enable viral intracellular and intercellular spread. Stable expression of the Potato leaf roll virus movement protein MP17 in Arabidopsis results in a carbohydrate export block and stunted growth. To identify host factors essential for viral infection, we screened a progeny population of EMS (ethyl methanesulfonate)-mutagenized Arabidopsis expressing a MP17:GFP fusion for suppressor mutants with restored wild type-like phenotype. Two suppressor mutants showed decreased susceptibility against Turnip mosaic virus and post-transcriptional silencing of MP17:GFP RNA in source leaves. Map based cloning identified in both lines mutations in XRN4 (Exoribonuclease 4), which was previously described as a suppressor of transgene silencing in source leaves. Importantly, silencing of MP17:GFP was not present in cotyledons and roots of the two suppressor mutants, which was confirmed in a third xrn4 T-DNA knock out line. Subsequent analysis of MP17:GFP transcript stability in xrn2 and xrn3 mutants indicated an essential role of AtXRN2 for silencing suppression in roots/cotyledons while AtXRN3 appears to act similar to AtXRN4 in source leaves, only. Overall, these findings point towards an organ-specific regulation of gene silencing in Arabidopsis.
21039566
Nitric oxide participates in cold-responsive phosphosphingolipid formation and gene expression in Arabidopsis thaliana.
Chilling triggers rapid molecular responses that permit the maintenance of plant cell homeostasis and plant adaptation. Recent data showed that nitric oxide (NO) is involved in plant acclimation and tolerance to cold. The participation of NO in the early transduction of the cold signal in Arabidopsis thaliana was investigated. The production of NO after a short exposure to cold was assessed using the NO-sensitive fluorescent probe 4, 5-diamino fluoresceine diacetate and chemiluminescence. Pharmacological and genetic approaches were used to analyze NO sources and NO-mediated changes in cold-regulated gene expression, phosphatidic acid (PtdOH) synthesis and sphingolipid phosphorylation. NO production was detected after 1-4h of chilling. It was impaired in the nia1nia2 nitrate reductase mutant. Moreover, NO accumulation was not observed in H7 plants overexpressing the A. thaliana nonsymbiotic hemoglobin Arabidopsis haemoglobin 1 (AHb1). Cold-regulated gene expression was affected in nia1nia2 and H7 plants. The synthesis of PtdOH upon chilling was not modified by NO depletion. By contrast, the formation of phytosphingosine phosphate and ceramide phosphate, two phosphorylated sphingolipids that are transiently synthesized upon chilling, was negatively regulated by NO. Taken together, these data suggest a new function for NO as an intermediate in gene regulation and lipid-based signaling during cold transduction.
21054438
The Arabidopsis tt19-4 mutant differentially accumulates proanthocyanidin and anthocyanin through a 3' amino acid substitution in glutathione S-transferase.
The Arabidopsis transparent testa (tt) mutant tt19-4 shows reduced seed coat colour, but stains darkly with DMACA and accumulates anthocyanins in aerial tissues. Positional cloning showed that tt19-4 was allelic to tt19-1 and has a G-to-T mutation in a conserved 3'-domain in the TT19-4 gene. Soluble and unextractable seed proanthocyanidins and hydrolysis of unextractable proanthocyanidin differ between wild-type Col-4 and both mutants. However, seed quercetins, unextractable proanthocyanidin hydrolysis, and seedling anthocyanin content, and flavonoid gene expression differ between tt19-1 and tt19-4. Transformation of tt19-1 with a TT19-4 cDNA results in vegetative anthocyanins, whereas TT19-4 cDNA cannot complement the proanthocyanidin and pale seed coat phenotype of tt19-1. Both recombinant TT19 and TT19-4 enzymes are functional GSTs and are localized in the cytosol, but TT19 did not function with wide range of flavonoids and natural products to produce conjugation products. We suggest that the dark seed coat of Arabidopsis is related to soluble proanthocyanidin content and that quercetin holds the key to the function of TT19. In addition, TT19 appears to have a 5' GSH-binding domain influencing both anthocyanin and proanthocyanidin accumulation and a 3' domain affecting proanthocyanidin accumulation by a single amino acid substitution.
21062318
Involvement of extracellular oxidative burst in salicylic acid-induced stomatal closure in Arabidopsis.
Salicylic acid (SA), a ubiquitous phenolic phytohormone, is involved in many plant physiological processes including stomatal movement. We analysed SA-induced stomatal closure, production of reactive oxygen species (ROS) and nitric oxide (NO), cytosolic calcium ion ([Ca^2+](cyt)) oscillations and inward-rectifying potassium (K+(in)) channel activity in Arabidopsis. SA-induced stomatal closure was inhibited by pre-treatment with catalase (CAT) and superoxide dismutase (SOD), suggesting the involvement of extracellular ROS. A peroxidase inhibitor, SHAM (salicylhydroxamic acid) completely abolished SA-induced stomatal closure whereas neither an inhibitor of NADPH oxidase (DPI) nor atrbohD atrbohF mutation impairs SA-induced stomatal closures. 3,3'-Diaminobenzidine (DAB) and nitroblue tetrazolium (NBT) stainings demonstrated that SA induced H2O2 and O2- production. Guard cell ROS accumulation was significantly increased by SA, but that ROS was suppressed by exogenous CAT, SOD and SHAM. NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) suppressed the SA-induced stomatal closure but did not suppress guard cell ROS accumulation whereas SHAM suppressed SA-induced NO production. SA failed to induce [Ca^2+](cyt) oscillations in guard cells whereas K+(in) channel activity was suppressed by SA. These results indicate that SA induces stomatal closure accompanied with extracellular ROS production mediated by SHAM-sensitive peroxidase, intracellular ROS accumulation and K+(in) channel inactivation.
21241326
Gene expression analysis of wounding-induced root-to-shoot communication in Arabidopsis thaliana.
Root-to-shoot communication plays an important role in the adaptation to environmental stress. In this study, we established a model system for root-to-shoot signalling to observe global gene expression in Arabidopsis thaliana. The roots of Arabidopsis seedlings were wounded and the expression in the shoots of 68 and 5 genes was up-regulated threefold at 30 min and 6 h post-injury, respectively. These genes were designated early and late Root-to-Shoot responsive (RtS) genes, respectively. Many of the early RtS genes were found to encode transcription factors such as AtERFs, whereas others were associated with jasmonic acid (JA) and ethylene (ET). Some of the late RtS genes were shown to be regulated by 12-oxo-phytodienoic acid (OPDA). In fact, elevated levels of JA and OPDA were detected in the shoots of seedlings 30 min and 6 h, respectively, after wounding of the roots. A mutant analysis revealed that JA and ET are involved in the expression of the early RtS genes. Thus, root-to-shoot communication for many RtS genes is associated with the systemic production of JA, OPDA and possibly ET.
21241328
Light exerts multiple levels of influence on the Arabidopsis wound response.
Light plays important roles in modulating plant responses to attack by pests and pathogens. Here, we test the hypothesis that darkness modifies the response to wounding, and examine possible mechanisms for such an effect. We investigated changes in the Arabidopsis transcriptome following a light-dark transition and the response to wounding either in the light or in the dark. The transcriptional response to the light-dark transition strongly resembles responses associated with carbon depletion. The dark shift and wound responses acted largely independently, but more complex interactions were identified at a number of levels. Darkness attenuates the overall transcriptional response to wounding, and we identified genes and physiological processes, such as anthocyanin accumulation, that exhibit light-dependent wound responses. Transcriptional activation of light-dependent wound-induced genes requires a chloroplast-derived signal originating from photosynthetic electron transport. We also present evidence of a role for the circadian clock in modifying wound responses. Our results show that darkness impacts on the wound response at a number of levels, which may imply differences in induced herbivore defences during the day and night.
21241330
The role of class A1 heat shock factors (HSFA1s) in response to heat and other stresses in Arabidopsis.
In Arabidopsis, there are four homologs of class A1 heat shock factor (HSFA1) genes, which likely encode the master regulators of heat shock response (HSR). However, previous studies with double knockout (KO) mutants were unable to confirm this point probably due to functional redundancy. Here, we generated a quadruple KO (QK) and four triple KO mutants to dissect their functions. Our data show that members of the HSFA1 group not only play a pivotal role in HSR but also are involved in growth and development. Alterations in morphology and retardation in growth were observed in the quadruple but not in triple KO mutants. The basal and acquired thermotolerance capacity was dramatically decreased in the QK mutant but varied in triple KO mutants at different developmental stages. The transcriptomics profiles suggested that more than 65% of the heat stress (HS)-up-regulated genes were HSFA1 dependent. HSFA1s were also involved in the expression of several HS genes induced by H(2) O(2) , salt and mannitol, which is consistent with the increased sensitive phenotype of the QK mutant to the stress factors. In conclusion, the Arabidopsis HSFA1s function as the master regulators of HSR and participate as important components in other abiotic stress responses as well.
21251017
A bicistronic, Ubiquitin-10 promoter-based vector cassette for transient transformation and functional analysis of membrane transport demonstrates the utility of quantitative voltage clamp studies on intact Arabidopsis root epidermis.
To date the use of fluorescent reporter constructs in analysing membrane transport has been limited primarily to cell lines expressing stably either the tagged transporter protein(s) or markers to identify lineages of interest. Strategies for transient expression have yet to be exploited in transport analysis, despite their wide application in cellular imaging studies. Here we describe a Gateway-compatible, bicistronic vector, incorporating the constitutive Ubiqutin-10 gene promoter of Arabidopsis that gives prolonged expression after transient transformation and enables fluorescence marking of cells without a fusion construct. We show that Arabidopsis root epidermal cells are readily transformed by co-cultivation with Agrobacterium and are tractable for quantitative electrophysiological analysis. As a proof of principle, we transiently transformed Arabidopsis with the bicistronic vector carrying GFP as the fluorescent marker and, separately, the integral plasma membrane protein SYP121 essential for the inward K+ channel current. We demonstrate that transient expression of SYP121 in syp121 mutant plants is sufficient to rescue the K+ current in vivo. The combination of transient expression and use of the bicistronic vector promises significant advantages for studies of membrane transport and nutrient acquisition in roots.
20840511
Hypoxia responsive gene expression is mediated by various subsets of transcription factors and miRNAs that are determined by the actual oxygen availability.
* Reduced oxygen availability is not only associated with flooding, but occurs also during growth and development. It is largely unknown how hypoxia is perceived and what signaling cascade is involved in activating adaptive responses. * We analysed the expression of over 1900 transcription factors (TFs) and 180 microRNA primary transcripts (pri-miRNAs) in Arabidopsis roots exposed to different hypoxic conditions by means of quantitative PCR. We also analysed the promoters of genes induced by hypoxia with respect to over-represented DNA elements that can act as potential TF binding sites and their in vivo interaction was verified. * We identified various subsets of TFs that responded differentially through time and in an oxygen concentration-dependent manner. The regulatory potential of selected TFs and their predicted DNA binding elements was validated. Although the expression of pri-miRNAs was differentially regulated under hypoxia, only one corresponding mature miRNA changed accordingly. Putative target transcripts of the miRNAs were not significantly affected. * Our results show that the regulation of hypoxia-induced genes is controlled via simultaneous interaction of various combinations of TFs. Under anoxic conditions, an additional set of TFs is induced. Regulation of gene expression via miRNAs appears to play a minor role during hypoxia.
21241331
Expression of a Brassica napus heme oxygenase confers plant tolerance to mercury toxicity.
Plant heme oxygenases (HOs) regulate biosynthesis of phytochrome which accounts for photo-acceptance and -morphogenesis. Recent studies have demonstrated that plant HOs also regulate many other physiological processes including response to environmental stimuli. To elucidate the mechanism by which HOs regulate plant adaptation to heavy metal exposure, three novel HOs genes were isolated from rapeseed (Brassica napus) and their expression patterns were analysed. Alignment of deduced protein sequences revealed that the three BnHOs share high identity with their corresponding orthologos (AtHO1-3) from Arabidopsis. To investigate whether the BnHO regulates plant tolerance to Hg toxicity, we constructed B. napus transgenic plants overexpressing BnHO-1. Under Hg stress, the transgenic plants had 1.41-1.59 folds higher biomass than the untransformants. However, overexpression of BnHO-1 resulted in less accumulation of Hg in some lines of transformants than in untransformants. The transgenic plants show lower abundance of reactive oxygen species and attenuated oxidative injury compared with the untransgenic plants. We cloned the promoter sequences of BnHO-1 from B. napus. Analysis revealed that the 1119 bp fragment contains a conserved Cd responsive element (CdRE) and others responding to multiple environmental stimuli. Transient expression in tobacco leaves showed differential responses to heavy metals (Zn, Cu, Pb, Hg and Cd).
20807375
OsEDR1 negatively regulates rice bacterial resistance via activation of ethylene biosynthesis.
Rice OsEDR1 is a sequence ortholog of Arabidopsis EDR1. However, its molecular function is unknown. We show here that OsEDR1-suppressing/knockout (KO) plants, which developed spontaneous lesions on the leaves, have enhanced resistance to Xanthomonas oryzae pv. oryzae (Xoo) causing bacterial blight disease. This resistance was associated with increased accumulation of salicylic acid (SA) and jasmonic acid (JA), induced expression of SA- and JA-related genes and suppressed accumulation of 1-aminocyclopropane-1-carboxylic acid (ACC), the direct precursor of ethylene, and expression of ethylene-related genes. OsEDR1-KO plants also showed suppressed production of ethylene. Knockout of OsEDR1 suppressed the ACC synthase (ACS) gene family, which encodes the rate-limiting enzymes of ethylene biosynthesis by catalysing the formation of ACC. The lesion phenotype and enhanced bacterial resistance of the OsEDR1-KO plants was partly complemented by the treatment with ACC. ACC treatment was associated with decreased SA and JA biosynthesis in OsEDR1-KO plants. In contrast, aminoethoxyvinylglycine, the inhibitor of ethylene biosynthesis, promoted expression of SA and JA synthesis-related genes in OsEDR1-KO plants. These results suggest that ethylene is a negative signalling molecule in rice bacterial resistance. In the rice-Xoo interaction, OsEDR1 transcriptionally promotes the synthesis of ethylene that, in turn, suppresses SA- and JA-associated defence signalling.
20955226
Separating parental environment from seed size effects on next generation growth and development in Arabidopsis.
Plant growth and development is profoundly influenced by environmental conditions that laboratory experimentation typically attempts to control. However, growth conditions are not uniform between or even within laboratories and the extent to which these differences influence plant growth and development is unknown. Experiments with wild-type Arabidopsis thaliana were designed to quantify the influences of parental environment and seed size on growth and development in the next generation. A single lot of seed was planted in six environmental chambers and grown to maturity. The seed produced was mechanically sieved into small and large size classes then grown in a common environment and subjected to a set of assays spanning the life cycle. Analysis of variance demonstrated that seed size effects were particularly significant early in development, affecting primary root growth and gravitropism, but also flowering time. Parental environment affected progeny germination time, flowering and weight of seed the progeny produced. In some cases, the parental environment affected the magnitude of (interacted with) the observed seed size effects. These data indicate that life history circumstances of the parental generation can affect growth and development throughout the life cycle of the next generation to an extent that should be considered when performing genetic studies.
21251018
Using tunable diode laser spectroscopy to measure carbon isotope discrimination and mesophyll conductance to CO2 diffusion dynamically at different CO2 concentrations.
In C3 leaves, the mesophyll conductance to CO2 diffusion, g(m) , determines the drawdown in CO2 concentration from intercellular airspace to the chloroplast stroma. Both g(m) and stomatal conductance limit photosynthetic rate and vary in response to the environment. We investigated the response of g(m) to changes in CO2 in two Arabidopsis genotypes (including a mutant with open stomata, ost1), tobacco and wheat. We combined measurements of gas exchange with carbon isotope discrimination using tunable diode laser absorption spectroscopy with a CO2 calibration system specially designed for a range of CO2 and O2 concentrations. CO2 was initially increased from 200 to 1000 ppm and then decreased stepwise to 200 ppm and increased stepwise back to 1000 ppm, or the sequence was reversed. In 2% O2 a step increase from 200 to 1000 ppm significantly decreased g(m) by 26-40% in all three species, whereas following a step decrease from 1000 to 200 ppm, the 26-38% increase in g(m) was not statistically significant. The response of g(m) to CO2 was less in 21% O2. Comparing wild type against the ost1 revealed that mesophyll and stomatal conductance varied independently in response to CO2. We discuss the effects of isotope fractionation factors on estimating g(m) .