GAPDH, NtOSAK and CDC48, a conserved chaperone-like AAA-ATPase, as nitric oxide targets in response to (a)biotic stresses

Abstract : Increasing evidences support the assumption that nitric oxide (NO) acts as a physiological mediator in plants facing (a)biotic stresses [1,2]. Understanding its effects requires a deep analysis of the molecular mechanisms underlying its mode of action. In the recent years, efforts have been made in identifying and understanding the function of plant proteins regulated by NO at the post-translational level, notably by S-nitrosylation [3]. We demonstrated that the glycolytic enzyme GAPDH undergoes a fast and transient S-nitrosylation in tobacco cells exposed to a salt stress [4]. S-nitrosylation affects only a small proportion of the GAPDH population and does not affect glycolysis. Interestingly, in vivo GAPDH interacts with the protein kinase NtOSAK (Nicotiana tabacum osmotic stress-activated protein kinase), a member of the SnRK2 protein kinase family previously shown to be rapidly activated through NO in response to (a)biotic stresses [5]. Our current hypothesis is that S-nitrosylated GAPDH might acts as a phosphor-relay recruiting protein substrates for NtOSAK.Besides GAPDH, we identified proteins undergoing S-nitrosylation in tobacco cell suspensions exposed to cryptogein, a 10 kDa protein produced by the oomycete Phytophthora cryptogea [6]. These proteins include CDC48, a conserved chaperone-like AAA-ATPases. Using a combination of structural and biochemical analysis, we provided evidence that NO induces a local conformational change within the protein and inhibits its enzymatic activity. The physiological incidence of this process will be discussed.