Roles of receptor-like cytoplasmic kinase VII members in pattern-triggered immune signaling

Pattern-recognition receptors (PRRs), which consist of receptor kinases (RKs) and receptor-like proteins (RLPs), sense microbial- and host-derived molecular patterns associated with pathogen infection to trigger immune responses in plants. Several kinases of the 46-member Arabidopsis thaliana receptor-like cytoplasmic kinase (RLCK) subfamily VII play important roles in pattern-triggered immunity, but it is unclear whether different RLCK VII members act specifically or redundantly in immune signaling. Here, we constructed nine higher order mutants of this subfamily (named rlck vii-1 to rlck vii-9) and systematically characterized their immune phenotypes. The mutants rlck vii-5, -7, and -8 had compromised reactive oxygen species (ROS) production in response to all patterns tested, indicating that the corresponding members are broadly required for signaling of multiple PRRs. However, rlck vii-4 was specifically defective in chitin-induced ROS production, suggesting that RCLK VII-4 members mediate the signaling of specific PRRs. Furthermore, RLCK VII-4 members were required for chitin-triggered activation of mitogen-activated protein kinase (MAPK), demonstrating that these kinases link a PRR to MAPK activation. Moreover, we found that RLCK VII-6 and -8 were also required for RK-mediated root growth. Together these results show that numerous RLCK VII members are involved in pattern-triggered immune signaling and uncover both common and specific roles of these kinases in plant development and immunity mediated by various RKs.