脱落酸 z-bo 2020-11-02 305

　　Abscisic acid (ABA), as one of the main plant hormones, participates in the growth and development of plants and the response to various biotic and abiotic stresses. Under adverse environmental stress, the ABA content in plant cells increases, which is a signal for plants to sense and respond to the external environment. Therefore, through the exploration and research of the molecular mechanism of the ABA signal transduction pathway, it is expected that related functional genes will be further explored and crops with excellent traits such as drought resistance and salt tolerance will be cultivated. Previous studies by Xie Qi, a researcher at the Institute of Genetics and Developmental Biology of the Chinese Academy of Sciences, and the laboratory of Pedro L. Rodriguez in Spain, respectively, found that the components of the ESCRTs (Endosome Sorting Complex Required for Transports) complexes involved in the intimal transport pathway were VPS23A and FYVE1 /FREE1, by recognizing the ABA receptor PYL4, can mediate the ABA receptor to enter the inner membrane transport pathway, thereby entering the vacuole for degradation, affecting the location of the ABA receptor and protein stability (Belda-Palazon et al., 2016; Yu et al., 2016). In the process of studying the involvement of VPS23A in regulating the ABA signaling pathway, Xie Qi's research group found that ABA treatment also affects the stability of VPS23A, thus starting the research in the field of protein stability of plant ESCRT complex components.

　　Xie Qi's research group found that VPS23A can be degraded through the 26S proteasome pathway, and it can be modified by the ubiquitin chain linked at position K48. The modification of the ubiquitin chain linked at position K48 causes the modified protein to enter the 26S proteasome pathway for degradation. Through IP/LC-MS-MS, a candidate protein XBAT35 that interacts with VPS23A was identified. XBAT35 is a RING type E3 ubiquitin ligase, which can interact with VPS23A. The xbat35 mutant exhibits a phenotype that is insensitive to ABA in terms of cotyledon greening and root growth, and the plant survival rate decreases under drought treatment; this is contrary to the phenotype of the vps23a mutant, which implies that XBAT35 is an E3 pan The ligase may negatively regulate the stability of VPS23A protein through ubiquitination modification. A series of biochemical experiments proved that XBAT35 can indeed promote the degradation of VPS23A protein, and XBAT35 can directly mediate the modification of the K48-linked ubiquitin chain of VPS23A. Therefore, VPS23A is a degradable ubiquitin substrate protein of XBAT35. Further experiments show that ABA promotes the degradation of VPS23A by XBAT35, thereby releasing the inhibitory effect of VPS23A on PYL4 protein, helping plants activate the ABA signaling pathway to respond to external environmental stress. This study further clarified the response and regulation mechanism of the ESCRT complex in ABA signal reception, and revealed the two main protein degradation pathways in plants, including the inner membrane transport degradation pathway and the ubiquitin proteasome degradation pathway involved in the ESCRT complex. By affecting the protein level of ABA receptors, the molecular mechanism of activation and deactivation of ABA signals is finely regulated.

　　The research results were published online in Molecular Plant (DOI: 10.1016/j.molp.2020.09.008). Yu Feifei, an assistant researcher in the Xie Qi group, and Ph.D. student Xiaoqiang Cao, are the co-first authors of the paper, and Xie Qi and Yu Feifei are the joint communication of the paper Author. The research work was funded by the National Key Research and Development Program and the National Natural Science Foundation of China.