Project description:Hydrogen peroxide (H2O2) signals regulate plant growth and defense by orchestrating genome-wide transcriptional re-programming, however, the specific mechanisms that regulate H2O2-dependent gene expression are poorly understood. Here we report the identification of the Mediator complex subunit MED8 as regulator of H2O2 responses, through a genetic screen of EAL4 promoter. Interestingly, the introduction of med8 mutation in the catalase-deficient background was associated with enhanced activation of salicylic acid biosynthesis and signaling pathways. Surprisingly, however, med8 seedlings were more tolerant to oxidative stress generated by methyl viologen. This tolerance phenotype is associated with the hyperactivation of defense and hormone signaling pathways in particular salicylic acid and jasmonic acid-related pathways. In addition, analysis of MED8 interactomes revealed interaction with novel pathways expanding Mediator complex function to processes beyond transcription, including miRNA biogenesis and and mRNA processing. We establish MED8 as a new component within the regulation of oxidative stress responses and demonstrate that MED8 act as negative regulator of H2O2 -driven activation of defense gene expression.
Project description:Arabidopsis is a host to the fungal powdery mildew pathogen, Erysiphe cichoracearum, and a nonhost to Blumeria graminis f.sp. hordei, the powdery mildew pathogenic on barley. A screen for mutants that allowed increased entry by this inappropriate or nonhost pathogen on Arabidopsis led to the identification of PEN3. While pen3 mutants permitted both increased penetration and increased hyphal growth by B. g. hordei, they were unexpectedly resistant to E. cichoracearum. This resistance was correlated with the appearance of chlorotic patches and was salicylic acid-dependent. Consistent with this observation, microarray analysis revealed that the salicylic acid defense pathway was hyper-induced in pen3 relative to wild type following inoculation with either E. cichoracearum or B. g. hordei. The pen3 phenotypes result from a loss of function of AtPDR8, a ubiquitously and highly expressed ATP binding cassette transporter. PEN3 protein tagged with green fluorescent protein localized to the plasma membrane in uninfected cells. In infected leaves, the protein concentrated to high levels at infection sites and surrounded fungal penetration pegs. We hypothesize that PEN3 may be involved in exporting toxic substrates to sites of infection and that accumulation of these substrates intracellularly in the pen3 mutant may secondarily activate the salicylic acid pathway. Keywords: disease state comparison
Project description:The goal of the microarray was to investigate the transcriptome changes induced by exogenous NAD+ in the wild-type Col-0 plants. Results showed that exogenous NAD+-induced dramatic transcriptional changes in Arabidopsis. Particularly, a large group of salicylic acid pathway genes including NPR1 and its traget genes were induced by NAD+, whereas the jasmonic acid/ethylene pathway defense marker gene PDF1.2 was inhibited by NAD+ treatment. In addition, a group of the pathogen-associated molecular pattern pathway genes were also induced by exogenous NAD+. These results indicate that exogenous NAD+ induces defense pathways against (hemi)biotrophic pathogens but suppresses defense against necrotrophs.
Project description:Expression profiling during arabidopsis/downy mildew interaction reveals a highly-expressed effector that attenuates responses to salicylic acid.
Project description:Myzus persicae (green peach aphid) feeding on Arabidopsis thaliana induces a defense response, quantified as reduced aphid progeny production, in infested leaves but not in other parts of the plant. Similarly, infiltration of aphid saliva into Arabidopsis leaves causes only a local increase in aphid resistance. Further characterization of the defense-eliciting salivary components indicates that Arabidopsis recognizes a proteinaceous elicitor with a size between 3 to 10 kD. Genetic analysis using well-characterized Arabidopsis mutant shows that saliva-induced resistance against M. persicae is independent of the known defense signaling pathways involving salicylic acid, jasmonate, and ethylene. Among 78 Arabidopsis genes that were induced by aphid saliva infiltration, 52 had been identified previously as aphid-induced, but few are responsive to the well-known plant defense signaling molecules salicylic acid and jasmonate. Quantitative PCR analysis confirms expression of saliva-induced genes. In particular, expression of a set of O-methyltransferases, which may be involved in the synthesis of aphid-repellent glucosinolates, was significantly up-regulated by both M. persicae feeding and treatment with aphid saliva. However, this did not correlate with increased production of 4-methoxyindol-3-ylmethylglucosinolate, suggesting that aphid salivary components trigger an Arabidopsis defense response that is independent of this aphid-deterrent glucosinolate.
Project description:Arabidopsis is a host to the fungal powdery mildew pathogen, Erysiphe cichoracearum, and a nonhost to Blumeria graminis f.sp. hordei, the powdery mildew pathogenic on barley. A screen for mutants that allowed increased entry by this inappropriate or nonhost pathogen on Arabidopsis led to the identification of PEN3. While pen3 mutants permitted both increased penetration and increased hyphal growth by B. g. hordei, they were unexpectedly resistant to E. cichoracearum. This resistance was correlated with the appearance of chlorotic patches and was salicylic acid-dependent. Consistent with this observation, microarray analysis revealed that the salicylic acid defense pathway was hyper-induced in pen3 relative to wild type following inoculation with either E. cichoracearum or B. g. hordei. The pen3 phenotypes result from a loss of function of AtPDR8, a ubiquitously and highly expressed ATP binding cassette transporter. PEN3 protein tagged with green fluorescent protein localized to the plasma membrane in uninfected cells. In infected leaves, the protein concentrated to high levels at infection sites and surrounded fungal penetration pegs. We hypothesize that PEN3 may be involved in exporting toxic substrates to sites of infection and that accumulation of these substrates intracellularly in the pen3 mutant may secondarily activate the salicylic acid pathway. Experiment Overall Design: Three week-old wild-type Col and mutant pen3 Arabidopsis thaliana plants were inoculated with Erysiphe cichoracearum, Blumeria graminis hordei, or not inoculated. 1 day post inoculation 16 rosettes were harvested per replicate. 4 replicates were perfomerd per treatment.
Project description:We found that amino acid transporter LHT1 was required for negatively regulating plant defence responses in addition to its physiological role in development and growth. In order to identify which defense pathways were involved in this process, we compared the expression profiles between wild type and lht1 mutant leaves without or with infection by Pseudomonas syringae pv. tomato DC3000 (Pst). In the lht1 mutant, except the changes in nitrogen metabolism-, cellular redox-, and photorespiration-associated gene expressions, the most drastic upregulations were found in the salicylic acid pathway-associated defense genes.
Project description:Myzus persicae (green peach aphid) feeding on Arabidopsis thaliana induces a defense response, quantified as reduced aphid progeny production, in infested leaves but not in other parts of the plant. Similarly, infiltration of aphid saliva into Arabidopsis leaves causes only a local increase in aphid resistance. Further characterization of the defense-eliciting salivary components indicates that Arabidopsis recognizes a proteinaceous elicitor with a size between 3 to 10 kD. Genetic analysis using well-characterized Arabidopsis mutant shows that saliva-induced resistance against M. persicae is independent of the known defense signaling pathways involving salicylic acid, jasmonate, and ethylene. Among 78 Arabidopsis genes that were induced by aphid saliva infiltration, 52 had been identified previously as aphid-induced, but few are responsive to the well-known plant defense signaling molecules salicylic acid and jasmonate. Quantitative PCR analysis confirms expression of saliva-induced genes. In particular, expression of a set of O-methyltransferases, which may be involved in the synthesis of aphid-repellent glucosinolates, was significantly up-regulated by both M. persicae feeding and treatment with aphid saliva. However, this did not correlate with increased production of 4-methoxyindol-3-ylmethylglucosinolate, suggesting that aphid salivary components trigger an Arabidopsis defense response that is independent of this aphid-deterrent glucosinolate. Experiment Overall Design: 3 biological replicates (control and treatment). Total number of samples: 6.