The MAP4 Kinase SIK1 Ensures Robust Extracellular ROS Burst and Antibacterial Immunity in Plants

Cell Host Microbe. 2018 Sep 12;24(3):379-391.e5. doi: 10.1016/j.chom.2018.08.007.


Microbial patterns are recognized by cell-surface receptors to initiate pattern-triggered immunity (PTI) in plants. Receptor-like cytoplasmic kinases (RLCKs), such as BIK1, and calcium-dependent protein kinases (CPKs) are engaged during PTI to activate the NADPH oxidase RBOHD for reactive oxygen species (ROS) production. It is unknown whether protein kinases besides CPKs and RLCKs participate in RBOHD regulation. We screened mutants in all ten Arabidopsis MAP4 kinases (MAP4Ks) and identified the conserved MAP4K SIK1 as a positive regulator of PTI. sik1 mutants were compromised in their ability to elicit the ROS burst in response to microbial features and exhibited compromised PTI to bacterial infection. SIK1 directly interacts with, phosphorylates, and stabilizes BIK1 in a kinase activity-dependent manner. Furthermore, SIK1 directly interacts with and phosphorylates RBOHD upon flagellin perception. Thus, SIK1 positively regulates immunity by stabilizing BIK1 and activating RBOHD to promote the extracellular ROS burst.

Keywords: BIK1; MAP4K; PTI; RBOHD; ROS; SIK1; autoimmunity; phosphorylation.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / enzymology*
  • Arabidopsis / genetics
  • Arabidopsis / immunology*
  • Arabidopsis / microbiology
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / immunology*
  • Gene Expression Regulation, Plant
  • NADPH Oxidases / genetics
  • NADPH Oxidases / immunology
  • Phosphorylation
  • Plant Diseases / immunology
  • Plant Diseases / microbiology
  • Plant Immunity
  • Protein-Serine-Threonine Kinases / genetics
  • Protein-Serine-Threonine Kinases / immunology*
  • Pseudomonas syringae / physiology
  • Reactive Oxygen Species / immunology*


  • Arabidopsis Proteins
  • Reactive Oxygen Species
  • respiratory burst oxidase homolog D, Arabidopsis
  • NADPH Oxidases
  • BIK1 protein, Arabidopsis
  • Protein-Serine-Threonine Kinases
  • SIK1 protein, Arabidopsis