Protein S-nitrosation differentially modulates tomato responses to infection by hemi-biotrophic oomycetes of Phytophthora spp.

Regulation of protein function by reversible S-nitrosation,a post-translational modification based on the attachment of nitroso group to cysteine thiols,has emerged among key mechanisms of NO signalling in plant development and stress responses.S-nitrosoglutathione is regarded as the most abundant low-molecular-weight S-nitrosothiol in plants,where its intracellular concentrations are modulated by S-nitrosoglutathione reductase.We analysed modulations of S-nitrosothiols and protein S-nitrosation mediated by S-nitrosoglutathione reductase in cultivated Solanum lycopersicum(susceptible)and wild Solanum habrochaites(resistant genotype)up to 96h post inoculation(hpi)by two hemibiotrophic oomycetes,Phytophthora infestans and Phytophthora parasitica.S-nitrosoglutathione reductase activity and protein level were decreased by P.infestans and P.parasitica infection in both genotypes,whereas protein S-nitrosothiols were increased by P.infestans infection,particularly at 72 hpi related to pathogen biotrophy–necrotrophy transition.Increased levels of S-nitrosothiols localised in both proximal and distal parts to the infection site,which suggests together with their localisation to vascular bundles a signalling role in systemic responses.S-nitrosation targets in plants infected with P.infestans identified by a proteomic analysis include namely antioxidant and defence proteins,together with important proteins of metabolic,regulatory and structural functions.Ascorbate peroxidase S-nitrosation was observed in both genotypes in parallel to increased enzyme activity and protein level during P.infestans pathogenesis,namely in the susceptible genotype.These results show important regulatory functions of protein S-nitrosation in concerting molecular mechanisms of plant resistance to hemibiotrophic pathogens.