H2O2 and in ensuring appropriate gene expression through both salicylic acid and jasmonic acid signaling pathways

GENOPLANTE programme " Redoxome ". Financial support of postgraduate students from the following sources is gratefully acknowledged: the Tunisian Ministry of Higher Education Abstract Glutathione is a major cellular thiol that is maintained in the reduced state by glutathione reductases (GR), which is encoded by two genes in Arabidopsis thaliana (GR1 and GR2). This study addressed the role of GR1 in H 2 O 2 responses through a combined genetic, transcriptomic, and redox profiling approach. To identify the potential role of changes in glutathione status in H 2 O 2 signaling, gr1 mutants, which show a constitutive increase in oxidized glutathione (GSSG), were compared with a catalase-deficient background (cat2), in which GSSG accumulation is conditionally driven by H 2 O 2. Parallel transcriptomics analysis of gr1 and cat2 identified overlapping gene expression profiles that in both lines were dependent on growth daylength. Overlapping genes included phytohormone-associated genes, in particular implicating glutathione oxidation state in the regulation of jasmonic acid signaling. Direct analysis of H 2 O 2-glutathione interactions in cat2 gr1 double mutants established that GR1-dependent glutathione status is required for multiple responses to increased H 2 O 2 availability, including limitation of lesion formation, accumulation of salicylic acid, induction of pathogenesis-related genes, and signaling through jasmonic acid pathways. Modulation of these responses in cat2 gr1 was linked to dramatic GSSG accumulation and modified expression of specific glutaredoxins and glutathione S-transferases, but little or no evidence of generalized oxidative stress or changes in thioredoxin-associated gene expression. We conclude that GR1 plays a crucial role in daylength-dependent redox signaling and that this function cannot be replaced by the second Arabidopsis glutathione reductase gene or by thiol systems such as the thioredoxin system. 5 Thiol-disulfide exchange plays crucial roles in protein structure, the regulation of enzymatic activity, and in redox signaling, and is principally mediated by thioredoxin (TRX) and glutathione reductase (GR)/glutathione systems (Buchanan and Balmer, 2005; Jacquot et al., 2008; Meyer et al., 2008). Arabidopsis lines identified in independent screens for alterations in heavy metal tolerance, meristem function, light signaling, and pathogen resistance have been shown to harbor mutations in the gene encoding the first enzyme of al., 2007). Studies on the rml1 mutant, which is severely deficient in glutathione synthesis, define a specific role for glutathione in root meristem function (Vernoux et al., 2000). However, shoot meristem function is regulated in a redundant manner by cytosolic glutathione and TRX (Reichheld …