Abstract
SNF1-related kinases 2 (SnRK2s) are central regulators of plant responses to environmental cues simultaneously playing a pivotal role in the plant development and growth in favorable conditions. They are activated in response to osmotic stress and some of them also to abscisic acid (ABA), the latter being key in ABA signaling. The SnRK2s can be viewed as molecular switches between growth and stress response; therefore, their activity is tightly regulated; needed only for a short time to trigger the response, it has to be induced transiently and otherwise kept at a very low level. This implies a strict and multifaceted control of SnRK2s in plant cells. Despite emerging new information concerning the regulation of SnRK2s, especially those involved in ABA signaling, a lot remains to be uncovered, the regulation of SnRK2s in an ABA-independent manner being particularly understudied. Here, we present an overview of available data, discuss some controversial issues, and provide our perspective on SnRK2 regulation.
Highlights
SnRK2 kinases from group 3 and 2 are activated by abscisic acid (ABA) via phosphorylation by Raf-like MAPKKK from subfamilies B2 and B3
Recent years have provided ample data on the regulation of ABA-responsive SnRK2s and ABA signaling by numerous mechanisms including phosphorylation, oxidation, S-nitrosylation, persulfidation, diverse protein–protein interactions, and degradation
This is a complex issue since SnRK2s regulate various processes, both normal plant growth and responses to diverse environmental stresses and, as we know, in several cases, the
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Twenty years of studies on SnRK2s have demonstrated that they are present in every plant species studied, from algae and mosses to higher plants, and provided ample data describing their role in the plant defense against harsh environments (e.g., drought, salinity, pathogen infection, stress induced by heavy metal ions) (for review, see [8,9,10,11]) Basing on their phylogeny, SnRK2s have been divided into three groups. Using various approaches, including phosphoproteomics, a large number of cellular targets of ABA-responsive SnRK2s have been identified, mostly proteins involved in stress responses Their activity, stability, and/or localization depends on phosphorylation, quite often the changes evoked by phosphorylation/dephosphorylation are transient, which is in line with the transient nature of SnRK2 activity.
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