Arabidopsis group C Raf-like protein kinases negatively regulate abscisic acid signaling and are direct substrates of SnRK2

Proc Natl Acad Sci U S A. 2021 Jul 27;118(30):e2100073118. doi: 10.1073/pnas.2100073118.

Abstract

The phytohormone abscisic acid (ABA) plays a major role in abiotic stress responses in plants, and subclass III SNF1-related protein kinase 2 (SnRK2) kinases mediate ABA signaling. In this study, we identified Raf36, a group C Raf-like protein kinase in Arabidopsis, as a protein that interacts with multiple SnRK2s. A series of reverse genetic and biochemical analyses revealed that 1) Raf36 negatively regulates ABA responses during postgermination growth, 2) the N terminus of Raf36 is directly phosphorylated by SnRK2s, and 3) Raf36 degradation is enhanced in response to ABA. In addition, Raf22, another C-type Raf-like kinase, functions partially redundantly with Raf36 to regulate ABA responses. A comparative phosphoproteomic analysis of ABA-induced responses of wild-type and raf22raf36-1 plants identified proteins that are phosphorylated downstream of Raf36 and Raf22 in planta. Together, these results support a model in which Raf36/Raf22 function mainly under optimal conditions to suppress ABA responses, whereas in response to ABA, the SnRK2 module promotes Raf36 degradation as a means of alleviating Raf36-dependent inhibition and allowing for heightened ABA signaling to occur.

Keywords: Arabidopsis thaliana; Raf-like kinase; SnRK2; abscisic acid.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Abscisic Acid / pharmacology*
  • Arabidopsis / genetics
  • Arabidopsis / growth & development
  • Arabidopsis / metabolism*
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism*
  • Gene Expression Regulation, Plant / drug effects*
  • Phosphorylation
  • Plant Growth Regulators / pharmacology
  • Protein Serine-Threonine Kinases / genetics
  • Protein Serine-Threonine Kinases / metabolism
  • Signal Transduction
  • Stress, Physiological*

Substances

  • Arabidopsis Proteins
  • Plant Growth Regulators
  • SnRK2 protein, Arabidopsis
  • Abscisic Acid
  • Protein Serine-Threonine Kinases