Microbe-associated molecular pattern-induced monoubiquitination of PRR complex-associated kinase BIK1 in Arabidopsis immunity.
L. SHAN (1), X. Ma (1), P. He (1) (1) Texas A&M University, U.S.A.

Prompt activation of pattern recognition receptors (PRRs) upon microbial infection is essential for hosts to defend against pathogen attacks. Plant BIK1 family receptor-like cytoplasmic kinases are key immune regulators associated with multiple PRRs, including flagellin receptor complex FLS2-BAK1 in Arabidopsis thaliana. Upon flagellin perception, BAK1 directly phosphorylates BIK1, leading to BIK1 dissociation from the FLS2-BAK1 complex to relay immune signaling. How BIK1 activation is regulated remains largely elusive. We report here that flagellin perception triggers rapid monoubiquitination of BIK1 and its homolog PBL1 in planta. An ubiquitination inhibitor PYR41 suppressed flagellin-induced multiple immune responses downstream of FLS2-BAK1 complex formation but upstream of BIK1 phosphorylation and dissociation from the FLS2-BAK1 complex. Time course and mutational analysis suggest that flagellin-induced BIK1 phosphorylation precedes its monoubiquitination. Mutational screen of individual lysine residues in BIK1 revealed that BIK1K204 plays an essential role in flagellin-induced BIK1 monoubiquitination and phosphorylation. Transgenic complementation assays indicate that BIK1K204 is crucial for BIK1-mediated plant immune signaling. Thus, our study suggests that monoubiquitination of a convergent immune regulator in multiple PRR complexes is coupled with plant immune signaling, and reveals the intertwined regulation of immune sensory complex activation by layered protein phosphorylation and ubiquitination.

Abstract Number: P17-608
Session Type: Poster