SCF ^AtPP2-B11 modulates ABA signaling by facilitating SnRK2.3 degradation in Arabidopsis thaliana

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.

Author summary

The phytohormone ABA plays critical roles in both plant growth and development and the response to environmental stimuli. The SnRK2s are important components of the PYR/PYL-ABA-PP2C regulatory machine which activate a set of bZIP transcription factors and ion transporters. However, the regulation of SnRK2 turnover is poorly understood. In this work, we show that SnRK2s are degraded by 26S proteasome and ABA promotes SnRK2.3 degradation. We also show that an F-box protein, AtPP2-B11, interacts with Arabidopsis Skp1-like protein ASK1 and ASK2, is a component of a SKP1/Cullin/F-box E3 ubiquitin ligase complex. AtPP2-B11 interacts and regulates the degradation of SnRK2.3 specifically. AtPP2-B11 is induced by ABA and knockdown of AtPP2-B11 expression markedly increases ABA sensitivity of plants during seed germination and post-germinative 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 mechanism through which AtPP2-B11 specifically degrades SnRK2.3 to attenuate the ABA signaling and plant responses to abiotic stress.