Small G Protein as a Novel Component of the Rice Bmssinosteroid Signal Transduction  

作　　者：Ge Zhang Xiaoguang Song Hongyan Guo Yao Wu Xiaoying Chen Rongxiang Fang 

机构地区：[1]State Key Laboratory of Plant Genomics, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China [2]National Center for Plant Gene Research (Beijing), Beijing 100101, China [3]University of Chinese Academy of Sciences, Beijing 100049, China [4]These authors contributed equally to this article. [5]Present address: State Key Laboratory of Plant Genomics and NationaT Center for Plant Gene Research (Beijing), Institute of Genetics and Developmental Biology,Chinese Academy of Sciences, Beijing 100101, China

出　　处：《Molecular Plant》2016年第9期1260-1271,共12页分子植物（英文版）

摘　　要：Brassinosteroids （BRs） are a class of steroid hormones that are essential for plant growth and development. The BR signal transduction pathway in the dicot model plantArabidopsis is well established, but the components connecting the BR signaling steps in rice have not been fully explored. For example, how the BR signaling is fine-tuned in rice, especially at the BR receptor level, is largely unknown. Here we show that OsPRA2, a rice small G protein, plays a repressive role in the BR signaling pathway. Lamina inclination, coleoptile elongation, and root inhibition assays indicated that rice plants with suppressed expression of OsPRA2 were more sensitive to exogenously applied brassinolide than the wild-type plants. Conversety, rice overexpressing OsPRA2 was less sensitive to exogenous brassinolide. Further study uncovered that OsPRA2 inhibited the dephosphorylation of, and thus inactivated the transcription factor BRASSINAZOLE- RESISTANT 1 （OsBZR1）. More importantly, OsPRA2 was found to co-localize with and directly bind to rice BR receptor BRASSlNOSTEROID-INSENSITIVE 1 （OsBRI1） at the plasma membrane. Additionally, the in vitro assays showed that OsPRA2 inhibits its autophosphorylation. This OsPRA2-OsBRI1 interaction led to the dissociation of OsBRI1 from its co-receptor OsBAK1, and abolished OsBRIl-mediated phosphorylation of OsBAK1. Together, these results reveal a possible working mechanism of OsPRA2 as a novel negative regu- lator on OsBRI1 and OsBZR1 and extend the knowledge about the regulatory mechanism of rice BR signaling.Brassinosteroids （BRs） are a class of steroid hormones that are essential for plant growth and development. The BR signal transduction pathway in the dicot model plantArabidopsis is well established, but the components connecting the BR signaling steps in rice have not been fully explored. For example, how the BR signaling is fine-tuned in rice, especially at the BR receptor level, is largely unknown. Here we show that OsPRA2, a rice small G protein, plays a repressive role in the BR signaling pathway. Lamina inclination, coleoptile elongation, and root inhibition assays indicated that rice plants with suppressed expression of OsPRA2 were more sensitive to exogenously applied brassinolide than the wild-type plants. Conversety, rice overexpressing OsPRA2 was less sensitive to exogenous brassinolide. Further study uncovered that OsPRA2 inhibited the dephosphorylation of, and thus inactivated the transcription factor BRASSINAZOLE- RESISTANT 1 （OsBZR1）. More importantly, OsPRA2 was found to co-localize with and directly bind to rice BR receptor BRASSlNOSTEROID-INSENSITIVE 1 （OsBRI1） at the plasma membrane. Additionally, the in vitro assays showed that OsPRA2 inhibits its autophosphorylation. This OsPRA2-OsBRI1 interaction led to the dissociation of OsBRI1 from its co-receptor OsBAK1, and abolished OsBRIl-mediated phosphorylation of OsBAK1. Together, these results reveal a possible working mechanism of OsPRA2 as a novel negative regu- lator on OsBRI1 and OsBZR1 and extend the knowledge about the regulatory mechanism of rice BR signaling.

关 键 词：BRASSINOSTEROID small G protein plant hormone signal transduction 

分 类 号：Q94[生物学—植物学]