Selective regulation of the chitin‐induced defense response by the Arabidopsis receptor‐like cytoplasmic kinase PBL27

Abstract

These authors contributed equally to this work. SUMMARYRecognition of microbe-associated molecular patterns (MAMPs) initiates pattern-triggered immunity in host plants. Pattern recognition receptors (PRRs) and receptor-like cytoplasmic kinases (RLCKs) are the major components required for sensing and transduction of these molecular patterns. However, the regulation of RLCKs by PRRs and their specificity remain obscure. In this study we show that PBL27, an Arabidopsis ortholog of OsRLCK185, is an immediate downstream component of the chitin receptor CERK1 and contributes to the regulation of chitin-induced immunity in Arabidopsis. Knockout of PBL27 resulted in the suppression of several chitin-induced defense responses, including the activation of MPK3/6 and callose deposition as well as in disease resistance against fungal and bacterial infections. On the other hand, the contribution of PBL27 to flg22 signaling appears to be very limited, suggesting that PBL27 selectively regulates defense signaling downstream of specific PRR complexes. In vitro phosphorylation experiments showed that CERK1 preferentially phosphorylated PBL27 in comparison to BIK1, whereas phosphorylation of PBL27 by BAK1 was very low compared with that of BIK1. Thus, the substrate specificity of the signaling receptor-like kinases, CERK1 and BAK1, may determine the preference of downstream RLCKs.

Two redundant receptor-like cytoplasmic kinases function downstream of pattern recognition receptors to regulate activation of SA biosynthesis in Arabidopsis

“…Several members in subfamily VII including BIK1, PBL1, and PBL27 have been shown to function as important signaling components in plant immunity (Lu et al, 2010;Kadota et al, 2014;Li et al, 2014;Ranf et al, 2014;Shinya et al, 2014). In this study, we found two additional members in this subfamily, PCRK1 and PCRK2, which are also required for plant defense Figure 6.…”

“…It is phosphorylated by OsCERK1 after chitin treatment and is required for chitin-induced immune responses. A recent study showed that PBL27, an Arabidopsis ortholog of OsRLCK185, regulates chitin-induced defense responses in Arabidopsis (Shinya et al, 2014).…”

PBL13 is a serine/threonine protein kinase that negatively regulates Arabidopsis immune responses.

“…Kinase-mediated immune regulation ranges from initial perception of MAMPs by transmembrane PRRs to mediating downstream immune signaling by RLCKs, calcium-dependent protein kinases, and MAPKs (Tena et al, 2011). The majority of characterized RLCK VII members function as positive regulators of MTI (Lu et al, 2010;Zhang et al, 2010;Yamaguchi et al, 2013;Ao et al, 2014;Shinya et al, 2014). In this study, we focused on the genetic and biochemical characterization of PBL13, an RLCK from subfamily VII possessing a unique C-terminal repeat motif.…”

“…RLCKs regulating MTI have been found to associate with PRR complexes and positively regulate immune responses in Arabidopsis and rice (Yamaguchi et al, 2013;Ao et al, 2014;Kadota et al, 2014;Li et al, 2014;Shinya et al, 2014). In light of the enhanced early MTI responses observed in the pbl13-2 KO, we reasoned that PBL13 may associate with PRR complexes to negatively regulate immune responses.…”

“…Analysis of BIK1 paralogs revealed that AvrPphB SUSCEPTIBLE1 (PBS1) and AvrPphB SUSCEPTIBLE1-LIKE1 (PBL1) function additively with BIK1 to regulate the ROS burst . RLCKs in subfamily VII have also been shown to be important for perception of chitin, a fungal MAMP Yamaguchi et al, 2013;Ao et al, 2014;Shinya et al, 2014). Rice (Oryza sativa) RLCK185, OsRLCK176, and Arabidopsis (Arabidopsis thaliana) PBL27 were also found to associate with the chitin coreceptor, indicating that RLCKs represent an important signaling module downstream of multiple PRR complexes (Yamaguchi et al, 2013;Ao et al, 2014;Shinya et al, 2014).…”