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

Yoshiaki KamiyamaMisaki HirotaniShinnosuke IshikawaFuko MinegishiSotaro KatagiriConner J RoganFuminori TakahashiMika NomotoKazuya IshikawaYutaka KodamaYasuomi TadaDaisuke TakezawaJeffrey C AndersonScott C PeckKazuo ShinozakiTaishi Umezawa
Published in: Proceedings of the National Academy of Sciences of the United States of America (2021)
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.
Keyphrases
  • transcription factor
  • arabidopsis thaliana
  • oxidative stress
  • gene expression
  • genome wide
  • binding protein
  • wild type
  • amino acid
  • cell wall