Tyrosine phosphorylation of protein kinase complex BAK1/BIK1 mediates Arabidopsis innate immunity

Abstract

The sessile plants have evolved a large number of receptor-like kinases (RLKs) and receptor-like cytoplasmic kinases (RLCKs) to modulate diverse biological processes, including plant innate immunity. Phosphorylation of the RLK/RLCK complex constitutes an essential step to initiate immune signaling. Two Arabidopsis plasma membrane-resident RLKs, flagellin-sensing 2 and brassinosteroid insensitive 1-associated kinase 1 (BAK1), interact with RLCK Botrytis-induced kinase 1 (BIK1) to initiate plant immune responses to bacterial flagellin. BAK1 directly phosphorylates BIK1 and positively regulates plant immunity. Classically defined as a serine/threonine kinase, BIK1 is shown here to possess tyrosine kinase activity with mass spectrometry, immunoblot, and genetic analyses. BIK1 is autophosphorylated at multiple tyrosine (Y) residues in addition to serine/threonine residues. Importantly, BAK1 is able to phosphorylate BIK1 at both tyrosine and serine/ threonine residues. BIK1Y150 is likely catalytically important as the mutation blocks both tyrosine and serine/threonine kinase activity, whereas Y243 and Y250 are more specifically involved in tyrosine phosphorylation. The BIK1 tyrosine phosphorylation plays a crucial role in BIK1-mediated plant innate immunity as the transgenic plants carrying BIK1Y150F, Y243F, or Y250F (the mutation of tyrosine to phenylalanine) failed to complement the bik1 mutant deficiency in immunity. Our data indicate that plant RLCK BIK1 is a nonreceptor dual-specificity kinase and both tyrosine and serine/ threonine kinase activities are required for its functions in plant immune signaling. Together with the previous finding of BAK1 to be autophosphorylated at tyrosine residues, our results unveiled the tyrosine phosphorylation cascade as a common regulatory mechanism that controls membrane-resident receptor signaling in plants and metazoans.

Phosphorylation of Trihelix Transcriptional Repressor ASR3 by MAP KINASE4 Negatively Regulates Arabidopsis Immunity

“…Treatment with calf intestinal alkaline phosphatase (CIP), a phosphatase that preferentially alters phosphotyrosine residues, did not significantly affect the flg22-induced ASR3 mobility shift, although it completely restored the mobility of phosphorylated BIK1 to that of the unmodified form ( Figure 2I) (Lu et al, 2010). This is consistent with the reports that BIK1 possesses tyrosine phosphorylation activity Lin et al, 2014). These results imply that ASR3 undergoes phosphorylation, likely on serine and/or threonine residues, upon flg22 perception.…”

Members of the Plant CRK Superfamily Are Capable of Trans- and Autophosphorylation of Tyrosine Residues

“…Therefore, the biochemical properties of CK1/CKLs might be different in plants from those in mammals. Many previous studies have suggested that several RLK/RLCKs such as BRASSINOSTEROID-INSENSITIVE 1 (BRI1) and BRI1-associated kinase 1 (BAK1) have Ser-, Thr-, and Tyrautophosphorylation activity (38,39). Our results revealed that the novel eight RLK/RLCKs identified have Tyr-autophosphorylation activity.…”

Tyrosine phosphorylation switching of a G protein

“…The DAVID bioinformatics resource (50,51) was used to analyze pathways shared by these LRR RLKs. Among them, LRR RLK family protein (PSY1R, AT1G72300, lane #19), LRR RLK family protein (AT5G37450, lane #66), LLR transmembrane protein kinase (GSO1, AT4G20140, lane #31), and PEP1 receptor 1 (PEPR1, AT1G73080, lane #20) are involved in protein tyrosine kinase signaling pathways, however, none of the four were previously reported to have tyrosine-protein kinase activity either in vivo or in vitro; BRI1-associated receptor kinase 1 (BAK1, AT4G33430, lane #12), LRR RLK family protein (BRI1, AT4G39400, lane #35), and somatic embryogenesis receptor-like kinase 1 (SERK1, AT1G71830, lane #18) are involved in the brassinosteroid mediated signaling pathway and are known dual-specificity kinases (27,52,53).…”