CALMODULIN-BINDING PROTEIN 60b plays dual roles in plant immunity.

SYSTEMIC ACQUIRED RESISTANCE DEFICIENT 1 (SARD1) and CALMODULIN-BINDING PROTEIN 60g (CBP60g) are two master transcription factors that regulate many defense-related genes in plant immunity. They are required for immunity downstream of the receptor-like protein SUPPRESSOR OF NPR1-1, CONSTITUTIVE 2 (SNC2). Constitutive defense responses in the gain-of-function autoimmune mutant are modestly affected in either or single mutants but completely suppressed in the double mutant. Here we report that CBP60b, another member of the CBP60 family, also functions as a positive regulator of SNC2-mediated immunity. Loss-of-function mutations of suppress the constitutive expression of and enhanced disease resistance in , whereas overexpression of leads to elevated expression and constitutive defense responses. In addition, transient expression of in activates the expression of the :: reporter gene. Chromatin immunoprecipitation assays further showed that CBP60b is recruited to the promoter region of , suggesting that it directly regulates expression. Interestingly, knocking out in the wild-type background leads to ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1)-dependent autoimmunity, suggesting that CBP60b is required for the expression of a guardee/decoy or a negative regulator of immunity mediated by receptors carrying an N-terminal Toll-interleukin-1 receptor-like domain.