CML9, an Arabidopsis calmodulin-like protein, contributes to plant innate immunity through a flagellin-dependent signalling pathway

Many stimuli such as hormones and elicitors induce changes in intracellular calcium levels to integrate information and activate appropriate responses. The Ca2+ signals are perceived by various Ca2+ sensors, and calmodulin (CaM) is one of the best characterized in eukaryotes. Calmodulin-like (CML) proteins extend the Ca2+ toolkit in plants; they share sequence similarity with the ubiquitous and highly conserved CaM but their roles at physiological and molecular levels are largely unknown. Knowledge of the contribution of Ca2+ decoding proteins to plant immunity is emerging, and we report here data on Arabidopsis thaliana CML9, whose expression is rapidly induced by phytopathogenic bacteria, flagellin and salicylic acid. Using a reverse genetic approach, we present evidence that CML9 is involved in plant defence by modulating responses to bacterial strains of Pseudomonas syringae. Compared to wild-type plants, the later responses normally observed upon flagellin application are altered in knockout mutants and over-expressing transgenic lines. Collectively, using PAMP treatment and P.similar to syringae strains, we have established that CML9 participates in plant innate immunity.