Abstract
The phytohormone abscisic acid (ABA) is an essential part of the plant response to abiotic stressors such as drought. Upon the perception of ABA, pyrabactin resistance (PYR)/PYR1-like (PYL)/regulatory components of ABA receptor (RCAR) proteins interact with co-receptor protein phosphatase type 2Cs to permit activation Snf1-related protein kinase2 (SnRK2) kinases, which switch on ABA signaling by phosphorylating various target proteins. Thus, SnRK2 kinases are central regulators of ABA signaling. However, the mechanisms that regulate SnRK2 degradation remain elusive. Here, we show that SnRK2.3 is degradated by 26S proteasome system and ABA promotes its degradation. We found that SnRK2.3 interacts with AtPP2-B11 directly. AtPP2-B11 is an F-box protein that is part of a SKP1/Cullin/F-box E3 ubiquitin ligase complex that negatively regulates plant responses to ABA by specifically promoting the degradation of SnRK2.3. AtPP2-B11 was induced by ABA, and the knockdown of AtPP2-B11 expression markedly increased the ABA sensitivity of plants during seed germination and postgerminative development. Overexpression of AtPP2-B11 does not affect ABA sensitivity, but inhibits the ABA hypersensitive phenotypes of SnRK2.3 overexpression lines. These results reveal a novel mechanism through which AtPP2-B11 specifically degrades SnRK2.3 to attenuate ABA signaling and the abiotic stress response in Arabidopsis.
Highlights
Abscisic acid (ABA) plays important roles in plant development and growth, including seed dormancy, seed germination, and postgerminative growth [1, 2]
The Snf1-related protein kinase2 (SnRK2) are important components of the pyrabactin resistance (PYR)/ PYL-ABA-PP2C regulatory machine which activate a set of bZIP transcription factors and ion transporters
We show that SnRK2s are degraded by 26S proteasome and ABA promotes SnRK2.3 degradation
Summary
Abscisic acid (ABA) plays important roles in plant development and growth, including seed dormancy, seed germination, and postgerminative growth [1, 2]. The discovery of the pyrabactin resistance (PYR)/PYR1-like (PYL)/regulatory components of ABA receptor (RCAR) protein family, which is comprised of ABA receptors, and intensive research into how these ABA receptors regulate plant responses to ABA have revealed much about the core ABA signaling pathway. This core pathway is mainly composed of PYR/PYL/ RCAR ABA receptors, their co-receptors (clade A phosphatase type 2Cs [PP2Cs]), and Snf1-related protein kinase (SnRK2) kinases, which phosphorylate bZIP transcription factors and ion channels to turn on ABA signaling [3,4,5]. A fundamental question is how the ABA signaling pathway is controlled via the regulation of SnRK2s activity
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