title: A Small G Protein as a Novel Component of the Rice Brassinosteroid Signal Transduction.
abstract: 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 plant Arabidopsis 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. Conversely, 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 BRASSINOSTEROID-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 OsBRI1-mediated phosphorylation of OsBAK1. Together, these results reveal a possible working mechanism of OsPRA2 as a novel negative regulator on OsBRI1 and OsBZR1 and extend the knowledge about the regulatory mechanism of rice BR signaling.
authors.affiliation: State Key Laboratory of Plant Genomics, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China; National Center for Plant Gene Research (Beijing), Beijing 100101, China; University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Ge
authors.initials: G
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Plant Genomics, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China; National Center for Plant Gene Research (Beijing), Beijing 100101, China.
authors.forename: Xiaoguang
authors.initials: X
authors.lastname: Song
authors.affiliation: State Key Laboratory of Plant Genomics, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China; National Center for Plant Gene Research (Beijing), Beijing 100101, China.
authors.forename: Hongyan
authors.initials: H
authors.lastname: Guo
authors.affiliation: State Key Laboratory of Plant Genomics, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China; National Center for Plant Gene Research (Beijing), Beijing 100101, China.
authors.forename: Yao
authors.initials: Y
authors.lastname: Wu
authors.affiliation: State Key Laboratory of Plant Genomics, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China; National Center for Plant Gene Research (Beijing), Beijing 100101, China. Electronic address: chenxy@im.ac.cn.
authors.forename: Xiaoying
authors.initials: X
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Plant Genomics, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China; National Center for Plant Gene Research (Beijing), Beijing 100101, China. Electronic address: fangrx@im.ac.cn.
authors.forename: Rongxiang
authors.initials: R
authors.lastname: Fang
mesh_terms: D060406:Brassinosteroids / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism*; D012275:Oryza / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D060406:Brassinosteroids; D010940:Plant Proteins; D020559:Monomeric GTP-Binding Proteins
keywords: brassinosteroid; plant hormone; signal transduction; small G protein