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Monomerization of abscisic acid receptors through CARKs-mediated phosphorylation

Xiaoyi Li1, Yiting Xie1, Qian Zhang1

  • 1Key Laboratory of Bio-Resources and Eco-Environment of Ministry of Education, College of Life Sciences, State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University, Chengdu, 610065, China.

The New Phytologist
|April 7, 2022
PubMed

Insights

Cytosolic ABA Receptor Kinase (CARK) proteins interact with ABA receptors, and CARK phosphorylation enhances ABA binding. This process triggers ABA responses, revealing a novel regulatory mechanism in plant stress signaling.

Area of Science:

  • Plant Biology
  • Molecular Signaling
  • Biochemistry

Background:

  • Cytosolic ABA Receptor Kinases (CARKs) are crucial for abscisic acid (ABA)-mediated stress responses.
  • The precise regulatory mechanisms of CARKs in ABA signaling pathways are not fully understood.

Purpose of the Study:

  • To elucidate the interaction network between CARKs and ABA receptors (RCARs/PYR1/PYLs).
  • To investigate the role of CARK-mediated phosphorylation in ABA receptor function and downstream signaling.
  • To uncover the regulatory feedback loops involving CARKs and ABA signaling components.

Main Methods:

  • Co-immunoprecipitation assays to determine CARK-RCAR interactions.
  • Isothermal titration calorimetry (ITC) to analyze ABA binding affinity.
  • In vitro kinase assays and phosphatase activity assays.
  • Generation and analysis of transgenic Arabidopsis plants expressing modified RCARs.
  • Chromatin immunoprecipitation followed by quantitative PCR (ChIP-qPCR) to assess transcription factor binding.

Main Results:

  • CARK4/5 interact with RCAR3 and RCAR11-RCAR14; CARK2/7/11 interact with RCAR11-RCAR14.
  • CARKs form homodimers and heterodimers in a kinase activity-dependent manner.
  • Phosphorylation of RCAR12 by CARK1 enhances ABA binding affinity.
  • Phosphorylated RCAR12 (RCAR12T105D) inhibits ABI1 phosphatase activity, upregulating ABA-responsive genes (RD29A, RD29B) and conferring ABA hypersensitivity.
  • Transcription factor ABI5 activates CARK1 and CARK3 expression by binding to their promoters' ABREs.

Conclusions:

  • CARKs function redundantly and differentially in ABA signaling.
  • Dimeric CARKs phosphorylate dimeric ABA receptors, leading to monomerization and activation of ABA responses.
  • A positive feedback loop exists where ABI5 activates CARK expression, reinforcing ABA signaling.
Keywords:
ABA receptorABI5CARKsabscisic acid (ABA)de-dimerizationphosphorylation

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