Selective regulation of the chitin‐induced defense response by the <scp>A</scp>rabidopsis receptor‐like cytoplasmic kinase <scp>PBL</scp>27

Abstract

Summary Recognition of microbe‐associated molecular patterns ( MAMP s) initiates pattern‐triggered immunity in host plants. Pattern recognition receptors ( PRR s) and receptor‐like cytoplasmic kinases ( RLCK s) are the major components required for sensing and transduction of these molecular patterns. However, the regulation of RLCK s by PRR s and their specificity remain obscure. In this study we show that PBL 27, an Arabidopsis ortholog of Os RLCK 185, is an immediate downstream component of the chitin receptor CERK 1 and contributes to the regulation of chitin‐induced immunity in Arabidopsis. Knockout of PBL 27 resulted in the suppression of several chitin‐induced defense responses, including the activation of MPK 3/6 and callose deposition as well as in disease resistance against fungal and bacterial infections. On the other hand, the contribution of PBL 27 to flg22 signaling appears to be very limited, suggesting that PBL 27 selectively regulates defense signaling downstream of specific PRR complexes. In vitro phosphorylation experiments showed that CERK 1 preferentially phosphorylated PBL 27 in comparison to BIK 1, whereas phosphorylation of PBL 27 by BAK 1 was very low compared with that of BIK 1. Thus, the substrate specificity of the signaling receptor‐like kinases, CERK 1 and BAK 1, may determine the preference of downstream RLCK s.