A Regulatory Module Controlling Homeostasis of a Plant Immune Kinase

Jinlong Wang, Lauren Grubb, Jiayu Wang, Xiangxiu Liang, Lin Li, Chulei Gao, Miaomiao Ma, Feng Feng, Meng Li, Lei Li, Xiaojuan Zhang, Feifei Yu, Qi Xie, She Chen, Cyril Zipfel, Jacqueline Monaghan, Jian-Min Zhou

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Abstract

Plant pattern recognition receptors (PRRs) perceive microbial and endogenous molecular patterns to activate immune signaling. The cytoplasmic kinase BIK1 acts downstream of multiple PRRs as a rate-limiting component, whose phosphorylation and accumulation are central to immune signal propagation. Previous work identified the calcium-dependent protein kinase CPK28 and heterotrimeric G proteins as negative and positive regulators of BIK1 accumulation, respectively. However, mechanisms underlying this regulation remain unknown. Here we show that the plant U-box proteins PUB25 and PUB26 are homologous E3 ligases that mark BIK1 for degradation to negatively regulate immunity. We demonstrate that the heterotrimeric G proteins inhibit PUB25/26 activity to stabilize BIK1, whereas CPK28 specifically phosphorylates conserved residues in PUB25/26 to enhance their activity and promote BIK1 degradation. Interestingly, PUB25/26 specifically target non-activated BIK1, suggesting that activated BIK1 is maintained for immune signaling. Our findings reveal a multi-protein regulatory module that enables robust yet tightly regulated immune responses.
Original languageEnglish
Pages (from-to)493-504.e6
JournalMolecular Cell
Volume69
Issue number3
Early online date18 Jan 2018
DOIs
Publication statusPublished - 1 Feb 2018

Keywords

  • innate immunity
  • ubiquitination
  • phosphorylation
  • heterotrimeric G proteins
  • calcium-dependent protein kinases
  • Arabidopsis
  • Pseudomonas syringae
  • Botrytis cinerea

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