S-Nitrosylation in plant defense

Abstract

Nitric oxide (NO) is an important signalling molecule in animal and plant defense responses. In the latter, the redox-active molecule NO has an essential role in restriction of pathogen attack by induction of defense genes and programmed host cell death. NO can react with the thiol group of cysteine residues to form S-nitrosothiols (S-nitrosylation). A number of NO-affected proteins in plants seem to be regulated by S-nitrosylation making this type of protein modification a predominant mechanism in NO-signalling. Recently, we demonstrated that NO is a redox regulator of a central transcriptional system for systemic acquired resistance in Arabidopsis thaliana. A change in the cellular redox status during the salicylic acid-mediated activation of defense leads to S-nitrosylation of the regulatory protein NPR1 and to its active monomeric form. Subsequently, the NPR1 monomers are translocated into the nucleus, where they interact with defense-associated transcription factors. Additional examples and evidences for NO-dependent modification of cysteine residues, describing its chemistry/formation, specificity, and possible physiological functions in plants will be discussed. The presentation underlines the importance of NO as a redox regulator.