Uncovering the role of S-nitrosylation in Jasmonic acid signalling during the plant immune response
Ayyar, Priya Vijay
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Plants have evolved a plethora of effective mechanisms to protect themselves from biotic stresses. Jasmonates (JAs) are employed as vital defence signals against both insect and pathogen attack. Jasmonic acid (JA) signalling plays a central role in plant defence and development. S-nitrosylation, a redox-based post-translational modification plays an important role in plant disease resistance. S-nitrosoglutathione (GSNO) is formed by the reaction of antioxidant glutathione (GSH) and nitric oxide (NO) and acts as a mobile reservoir of NO bioactivity. The Arabidopsis thaliana S-NITROSOGLUTATHIONE REDUCTASE (AtGSNOR1) controls multiple modes of disease resistance via S-nitrosylation. In this context, the Arabidopsis lossof- function mutant atgsnor1-3 exhibits higher susceptibility to Botrytis cinerea a necrotrophic pathogens and Pieris rapae insect attack. Accumulation of JA was reduced in atgsnor1-3 after mechanical wounding. JA marker genes were also downregulated in atgsnor1-3 compared to Col-0 after Methyl Jasmonate (Me-JA) treatment. The relative gene expression of Vegetative Storage Protein (VSP) was reduced in atgsnor1-3 compared to wild type. Further, protein-protein interaction experiments in yeast two hybrid assays revealed an inhibition of Coronatine-insensitive 1 (COI1) and Jasmonate ZIM domain (JAZ1) interactions upon NO donor application. Interestingly it was also shown that Nitric oxide donor may inhibited the degradation of JAZ1-β-glucoronidase (GUS) fusion protein driven by a CaMV35s:: JAZ1-GUS transgene in GUS histochemical analysis but not in flurometric assay. A biotin switch assay of recombinant JAZ1-Maltose-binding protein (MBP) has shown that JAZ1-MBP was S-nitrosylated and mass spectrometry suggested Cysteine229 (Cys229) was the site of this modification. Further, CaMV35S::JAZ1-Flag transgene expressed in either a wild-type or atgsnor1-3 genetic background, suggested that JAZ1 was S-nitrosylated in vivo. Collectively, our data imply that JA-signalling engaged in response to either insect predation or attempted B. cinerea infection is under redox control as high SNO in atgsnor1-3 has disrupted the JA signalling pathway. Furthermore, our data suggest that S-nitrosylation of Cys-229 of JAZ1 may control JA-mediated signalling by blocking the interaction of this protein with COI1, thus reducing the turnover of JAZ1 by the 26S proteasome and consequently enabling continued JAZ1-mediated repression of JA-dependent gene expression in the presence of Me-JA. Thus our findings highlight the importance of NO and associated S-nitrosylation in JA signalling during plant immune response.