The plant hormone abscisic acid (ABA) is an important regulator in plant abiotic stress adaptation. The control of co-receptor PP2C protein like ABI1 is the central hub of ABA signal transduction. Under standard conditions, ABI1 binds to protein kinase SnRK2s and inhibits its activity. ABA bound to the receptor protein PYR1/PYLs competes with SnRK2s in targeting ABI1, thereby releasing SnRK2s and activating the ABA response.
The research team led by Professor Xie Qi from the Institute of Genetics and Developmental Biology of the Chinese Academy of Sciences has long been studying ubiquitination, a post-translational modification mechanism that regulates ABA signaling. Their previous work revealed the endocytosis of PYL4 mediated by the ubiquitination of the E2-like protein VPS23, and ABA promotes XBAT35 to degrade VPS23A, thereby releasing the inhibitory effect on the ABA receptor PYL4. However, whether ABA signaling involves specific E2 proteins required for ubiquitination, and how ABA signaling regulates ubiquitination is not yet fully understood.
Recently, they identified a specific E2 enzyme UBC27, which positively regulates drought tolerance and ABA response in plants. Through IP/MS analysis, they determined that ABA co-receptor ABI1 and RING-type E3 ligase AIRP3 are interacting proteins of UBC27.
They found that UBC27 interacts with ABI1 and promotes its degradation, and activates the E3 activity of AIRP3. AIRP3 acts as the E3 ligase of ABI1.
In addition, ABI1 exerts the epistasis of UBC27 and AIRP3, while the function of AIRP3 is UBC27-dependent. In addition, ABA treatment induces the expression of UBC27, inhibits the degradation of UBC27, and enhances the interaction between UBC27 and ABI1.
These results reveal the new E2-E3 complex in the degradation of ABI1 and the important and complex regulation of ABA signaling by the ubiquitination system.
The title of the paper is “UBC27-AIRP3 ubiquitination complex regulates ABA signaling by promoting the degradation of ABI1 in Arabidopsis thaliana.” It was published online on PNAS on October 19, 2020.
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