A Tyrosine Phosphorylation Cycle of a Plant Receptor Ser/Thr Kinase Controls the on and Off of Chitin Signaling

Abstract

Plants initiate immunity by cell surface pattern-recognition receptors (PRRs) perceiving non-self molecules. PRRs are mostly receptor serine/threonine (Ser/Thr) kinases evolutionarily related to animal interleukin-1 receptor-associated kinase (IRAK)/Pelle-soluble kinases. However, how the activity of these receptor kinases is modulated remains poorly understood. Here, we report that the Arabidopsis PRR CHITIN ELICITOR RECEPTER KINASE 1 (CERK1) undergoes autophosphorylation in unelicited cells at tyrosine428 (Tyr428), which is indispensable for the chitin-induced CERK1 activation. Chitin-activated CERK1 recruits the CERK1-INTERACTING PROTEIN PHOSPHATASE 1 (CIPP1), a predicted Ser/Thr phosphatase, to dephosphorylate Tyr428 and phase out the activity of CERK1. CIPP1 dissociates from Tyr428- dephosphorylated CERK1, allowing CERK1 to return the standby state by retrieving Tyr428 autophosphorylation. Our work sheds multiple mechanistic insights into plant chitin signaling and provides an unprecedented example that a pair of receptor Ser/Thr kinase and Ser/Thr phosphatase, both with unexpected dual specificity, coordinate to dynamically regulate signal transduction through a Tyr phosphorylation cycle.