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

Summary Many stimuli such as hormones and elicitors induce changes in intracellular calcium levels to integrate information and activate appropriate responses. The Ca 2+ signals are perceived by various Ca 2+ sensors, and calmodulin (CaM) is one of the best characterized in eukaryotes. Calmodulin‐like (CML) proteins extend the Ca 2+ 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 Ca 2+ 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. syringae strains, we have established that CML9 participates in plant innate immunity.