The Mediator kinase module serves as a positive regulator of salicylic acid accumulation and systemic acquired resistance

Summary In plants, the calmodulin‐binding transcription activators ( CAMTA s) are required for transcriptional regulation of abiotic and biotic stress responses. Among them, CAMTA 3 in Arabidopsis has been intensively studied and shown to function redundantly with CAMTA 1 and CAMTA 2 to negatively regulate plant immunity. The camta1/2/3 triple mutant accordingly exhibits severe dwarfism due to autoimmunity. Here, through a suppressor screen using camta1/2/3 triple mutant, we found that a mutation in Cyclin‐Dependent Kinase 8 ( CDK 8 ) partially suppresses the dwarfism and constitutive resistance phenotypes of camta1/2/3 . CDK 8 positively regulates steady‐state salicylic acid ( SA ) levels and systemic required resistance ( SAR ). The expression of SA biosynthesis genes such as ICS 1 and EDS 5 is down‐regulated in cdk8 mutants under uninfected conditions, suggesting that CDK 8 contributes to the transcriptional regulation of these SA pathway genes. Knocking out another Mediator kinase module member MED 12 yielded similar defects including decreased steady‐state SA level and compromised SAR , suggesting that the whole Mediator kinase module contributes to the transcriptional regulation of SA levels and SAR .