Positive And Negative Regulation Of Defense Responses Against Pseudomonas Syringae In Arabidopsis

Abstract

Immune signaling in plants involves both positive and negative regulators. Maintaining a balance between growth and defense responses is important because there is a fitness cost to the plants if immune responses are left unchecked. Suppression of immune responses in the absence of pathogens as well as after the threat has passed is critical in maintaining such a balance between growth and defense responses. Upon pathogen perception, the positive regulators counter the immune repression to induce defense responses. We investigated the roles of two genes, <italic>CBP60a <italic> and <italic>PCRK1 <italic> in the regulation of defense responses against <italic>Pseudomonas syringae <italic> pathogen in the model system <italic>Arabidopsis thaliana <italic>. CBP60a is a negative regulator of immune responses. We showed that CBP60a is a CaM binding protein and that CaM binding is important for its function in transducing defense signals. Mutants of CBP60a were more resistant to <italic>Pseudomonas syringae <italic> infection suggesting that CBP60a was a negative regulator of defense responses. We found that CBP60a functions in repressing immune signaling under conditions where the plants are not challenged by a pathogen. We also investigated the role of a putative kinase, PCRK1, in immune signaling. We showed that <italic>pcrk1<italic> mutants are more susceptible to <italic>Pseudomonas syringae <italic> than wild type plants suggesting that PCRK1 has a positive role in immune responses. We also showed that PCRK1 is important for immunity triggered by some of the conserved Microbe Associated Molecular Patterns (MAMP) as well endogenous signals generated as a result of pathogen activity called Damage Associated Molecular Patterns (DAMP).