Plant Raf-like kinases regulate the mRNA population upstream of ABA-unresponsive SnRK2 kinases under drought stress

Fumiyuki Soma,Takamasa Suzuki,Kazuko Yamaguchi-Shinozaki,Kazuo Shinozaki,Fuminori Takahashi

doi:10.1038/s41467-020-15239-3

Abstract

SNF1-related protein kinases 2 (SnRK2s) are key regulators governing the plant adaptive responses to osmotic stresses, such as drought and high salinity. Subclass III SnRK2s function as central regulators of abscisic acid (ABA) signalling and orchestrate ABA-regulated adaptive responses to osmotic stresses. Seed plants have acquired other types of osmotic stress-activated but ABA-unresponsive subclass I SnRK2s that regulate mRNA decay and promote plant growth under osmotic stresses. In contrast to subclass III SnRK2s, the regulatory mechanisms underlying the rapid activation of subclass I SnRK2s in response to osmotic stress remain elusive. Here, we report that three B4 Raf-like MAP kinase kinase kinases (MAPKKKs) phosphorylate and activate subclass I SnRK2s under osmotic stress. Transcriptome analyses reveal that genes downstream of these MAPKKKs largely overlap with subclass I SnRK2-regulated genes under osmotic stress, which indicates that these MAPKKKs are upstream factors of subclass I SnRK2 and are directly activated by osmotic stress.

Highlights

SNF1-related protein kinases 2 (SnRK2s) are key regulators governing the plant adaptive responses to osmotic stresses, such as drought and high salinity
Previous studies showed that these three Raf-like kinases were phosphorylated during the early stages of the osmotic stress response of plants[25]. We focused on these three Raf-like kinases RAF18, RAF20 and RAF24
Since subclass I SNF1-related protein kinase 2 (SnRK2) are rapidly activated in response to osmotic stress, we performed LC-MS/MS analyses to identify subclass I SnRK2interacting proteins in plants that were treated with 800 mM mannitol for a short time (10 min) (Fig. 1a)

Summary

Introduction

SNF1-related protein kinases 2 (SnRK2s) are key regulators governing the plant adaptive responses to osmotic stresses, such as drought and high salinity. The “ABA-activated subclass III SnRK2s-AREB/ABF” signalling module is known to function as the transcriptional activation system in ABA-responsive gene expression in from mosses to seed plants[23]. To enhance their adaptability under constitutively changing stress conditions[20], seed plants are thought to have acquired a post-transcriptional regulation system mediated by the “ABA-unresponsive subclass I SnRK2s-VARICOSE” signalling module, which promotes marked changes in the mRNA populations under osmotic stress conditions, in addition to the transcriptional activation system during the process of evolution. Three B4 Raf-like MAP kinase kinase kinases (B4 Raf-like MAPKKKs) are identified as upstream factors of the ABA-unresponsive subclass I SnRK2-VCS signalling pathway that are activated by osmotic stress

Methods

Results

Conclusion