RLK185, Interacting With BAK1and BIK1,Mediates Plant Innate Immunity Responses

The Arabidopsis genome possesses more than600receptor like kinases (RLKs). RLKs regulate many signaling programs including BR response, innate immunity, self-incompatibility and cell growth and development. BAK1, a member of LRR-RLKs, functions as a co-receptor of the BR receptor BRI1to regulate BR perception and signal transduction, and a co-receptor of FLS2and EFR to respond bacterial peptide ligands flg22and elf18, respectively.To reveal unknown proteins interacting with BAK1, we used mating based split ubiquitin system to test the interaction between BAK1and the members of LRR-RLK Xand XI family. We proved some known interaction models (BRI1/BAK1> BIR1/BAK1) and also found some unpublished interaction models (GSO1/BAK1, PSY/BAK1, CLV1/BAK1, BAM2/BAK1). Considering the mutants’phenotype caused by bakl and its homologues, we assumed that BAK1can regulate the formation of epidermis, development of embryo, maintenance and differentiation of shoot apical meristem. In addition, we found several functionally undefined LRR-RLKs can interact with BAK1in vivo.AT5G25930, a member of LRR-RLK XI family, containing22LRRs, was named as RLK185whose function is not yet known. RLK185interacts with BAK1in yeast and in tobacco leaves. RLK185interacts with several paralogs of BAK1, and the interactions are independent of the cytoplasmic domain of RLK185. RLK185contains an active catalytic domain. GUS staining result shows that RLK185is mainly expressed in roots, mature and senescence leaves, and abscission zones of floral organs. After inoculation of crude protein from Pst DC3000into the leaves of transgenic plant carrying the construct of proRLK185:NLS-YFP, we observed more fluorescence spots compared with that of inoculation of mock solution, suggesting that crude protein can induce the expression of RLK185. Interestingly, RLK185interacts with BIK1, PBS1and PBL2, which are proved to function in innate immunity signaling, suggesting that RLK185is a novel LRR-RLK involving in innate immunity response, similar to the functions of FLS2.