RECEPTOR-LIKE KINASE 902 Associates with and Phosphorylates BRASSINOSTEROID-SIGNALING KINASE1 to Regulate Plant Immunity

Abstract

Plants employ receptor-like kinases (RLKs) and receptor-like proteins for rapid recognition of invading pathogens, and RLKs then transmit signals to receptor-like cytoplasmic kinases (RLCKs) to activate immune responses. RLKs are under fine regulation mediated by subcellular trafficking, which contributes to proper activation of plant immunity. In this study, we show that Arabidopsis thaliana RECEPTOR-LIKE KINASE 902 (RLK902) plays important roles in resistance to the bacterial pathogen Pseudomonas syringae, but not to the fungal powdery mildew pathogen Golovinomyces cichoracearum. RLK902 localizes at the plasma membrane and associates with ENHANCED DISEASE RESISTANCE 4 (EDR4), a protein involved in clathrin-mediated trafficking pathways. EDR4 and CLATHRIN HEAVY CHAIN 2 (CHC2) regulate the subcellular trafficking and accumulation of RLK902 protein. Furthermore, we found that RLK902 directly associates with the RLCK BRASSINOSTEROID-SIGNALING KINASE1 (BSK1), a key component of plant immunity, but not with other members of the FLAGELLIN SENSING 2 immune complex. RLK902 phosphorylates BSK1, and its Ser-230 is a key phosphorylation site critical for RLK902-mediated defense signaling. Taken together, our data indicate that EDR4 regulates plant immunity by modulating the subcellular trafficking and protein accumulation of RLK902, and that RLK902 transmits immune signals by phosphorylating BSK1.

Plant immune signaling: Advancing on two frontiers

“…Importantly, four LRR‐RLKs subnetworks were identified in CSI LRR and three of them contain a LRR‐RLK protein as the most interconnected and important node of each subnetwork, including BAK1, APEX, and RLK902, suggesting that plants have evolved small numbers of RLKs to connect their otherwise unconnected larger counterparts (Smakowska‐Luzan et al 2018). The Arabidopsis RLK902, a member of the LRR III subfamily of RLKs with only five LRRs at its N terminus, was recently shown to localize at the PM and play an essential role in resistance to the bacterial pathogen P. syringae (Zhao et al 2019).…”

“…In rice, the BIK1 orthologs OsRLCK176 and OsRLCK185 were shown to associate with OsCERK1 to mediate the chitin and peptidoglycan‐triggered immune signaling (Couto and Zipfel 2016; Li et al 2017). In addition to the RLCK group VII members, Arabidopsis RLCK group XII members BR‐SIGNALING KINASE 1 (BSK1) and BSK5 have also been reported to play a crucial role in PTI by interacting with PRRs directly (Shi et al 2013; Majhi et al 2019; Zhao et al 2019).…”

Mai1 protein acts between host recognition of pathogen effectors and MAPK signaling

“…BSK proteins lack key amino acids that are required for kinase activity, and thus have been predicted to be pseudokinases with putative roles as scaffold proteins (42)(43)(44). Although AtBSK1 also lacks these motifs, three papers, report that AtBSK1 autophosphorylates and can transphosphorylate AtMAPKKK5, and that the ATP binding site was required for its role in resistance to a fungal pathogen and PTI (39,40,45). We attempted to reproduce the kinase activity reported for AtBSK1 but were unable to see activity under our kinase assay conditions or those used for AtBSK1 (45) (Fig.…”

“…S3D, cell pellets were resuspended in column buffer and lysed by sonication. The cell lysate was mixed with the appropriate resin, and proteins were eluted with 50 mM reduced glutathione.Kinase assays were performed for 30 minutes at room temperature in 20 µL of kinase reaction buffer (50mM HEPES, pH 7.5, 10mM MgCl2 and/or 10mM MnCl2 and/or 10mM CaCl2, and 3 µg myelin basic protein) containing 2 µCi [γ-32 P], or were performed exactly as described in(45), using 5 µg of each of the proteins. Reactions were stopped by adding SDS-PAGE sample buffer.…”

An ankyrin-repeat and WRKY-domain-containing immune receptor confers stripe rust resistance in wheat

“…Different plasmids transformed into Agrobacterium tumefaciens GV3101 were suspended in infiltration buffer as previously described 50 to OD 600 = 1.5. Transient expression, total protein extraction and immunoblot analysis were performed as described 51 , with minor alterations. Total protein extracts (1 ml) were incubated with 20 μL agarose-conjugated anti-GFP antibody (MBL, D153-8) at 4°C for 4 h with gentle rotation.…”