Regulation of plant immunity through ubiquitin-mediated modulation of Ca(2+) -calmodulin-AtSR1/CAMTA3 signaling

Plant J. 2014 Apr;78(2):269-81. doi: 10.1111/tpj.12473. Epub 2014 Mar 26.

Abstract

Transient changes in intracellular Ca(2+) concentration are essential signals for activation of plant immunity. It has also been reported that Ca(2+) signals suppress salicylic acid-mediated plant defense through AtSR1/CAMTA3, a member of the Ca(2+) /calmodulin-regulated transcription factor family that is conserved in multicellular eukaryotes. How plants overcome this negative regulation to mount an effective defense response during a stage of intracellular Ca(2+) surge is unclear. Here we report the identification and functional characterization of an important component of ubiquitin ligase, and the associated AtSR1 turnover. The AtSR1 interaction protein 1 (SR1IP1) was identified by CytoTrap two-hybrid screening. The loss-of-function mutant of SR1IP1 is more susceptible to bacterial pathogens, and over-expression of SR1IP1 confers enhanced resistance, indicating that SR1IP1 acts as a positive regulator of plant defense. SR1IP1 and AtSR1 act in the same signaling pathway to regulate plant immunity. SR1IP1 contains the structural features of a substrate adaptor in cullin 3-based E3 ubiquitin ligase, and was shown to serve as a substrate adaptor that recruits AtSR1 for ubiquitination and degradation when plants are challenged with pathogens. Hence, SR1IP1 positively regulates plant immunity by removing the defense suppressor AtSR1. These findings provide a mechanistic insight into how Ca(2+) -mediated actions are coordinated to achieve effective plant immunity.

Keywords: Arabidopsis thaliana; Pseudomonas syringae; calcium/calmodulin; plant defense; salicylic acid; ubiquitin.

MeSH terms

  • Arabidopsis / genetics
  • Arabidopsis / immunology*
  • Arabidopsis / metabolism
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism
  • Arabidopsis Proteins / physiology*
  • Calcium Signaling*
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism
  • Carrier Proteins / physiology
  • Cullin Proteins
  • Host-Pathogen Interactions
  • Plant Immunity*
  • Proteasome Endopeptidase Complex / metabolism
  • Proteolysis
  • Pseudomonas syringae / physiology
  • Transcription Factors / metabolism
  • Transcription Factors / physiology*
  • Ubiquitin / metabolism
  • Ubiquitin / physiology*
  • Ubiquitination

Substances

  • AT1G26830 protein, Arabidopsis
  • Arabidopsis Proteins
  • CAMTA3 protein, Arabidopsis
  • Carrier Proteins
  • Cullin Proteins
  • SR1 protein, Arabidopsis
  • SR1IP1 protein, Arabidopsis
  • Transcription Factors
  • Ubiquitin
  • Proteasome Endopeptidase Complex