GSK2 stabilizes OFP3 to suppress brassinosteroid responses in rice. (13th February 2020)

• Record Type: Journal Article
• Authors: Xiao, Yunhua; Zhang, Guoxia; Liu, Dapu; Niu, Mei; Tong, Hongning; Chu, Chengcai
• Is Part Of: Plant journal. Volume 102:Number 6(2020)
• Page Start: 1187
• Page End: 1201
• Publication Date: 2020-02-13
• Subjects: brassinosteroid -- DLT -- grain size -- GSK2 -- leaf angle -- OFP3 -- plant height -- rice (Oryza sativa); Plant molecular biology -- Periodicals; Plant cells and tissues -- Periodicals; Botany -- Periodicals; 580
• DOI: 10.1111/tpj.14692
• Languages: English
• ISSNs: 0960-7412

Abstract

Summary: Brassinosteroids (BRs) are a class of phytohormones that modulate several important agronomic traits in rice ( Oryza sativa ). GSK2 is one of the critical suppressors of BR signalling and targets transcription factors such as OsBZR1 and DLT to regulate BR responses. Here, we identified OFP3 (OVATE FAMILY PROTEIN 3) as an interactor of both GSK2 and DLT by yeast‐two‐hybrid screening and demonstrated that OFP3 plays a distinctly negative role in BR responses. While knockout of OFP3 promoted rice seedling growth, overexpression of OFP3 led to strong BR insensitivity, which resulted in reduced plant height, leaf angle, and grain size. Interestingly, both BR biosynthetic and signalling genes had decreased expression in the overexpression plants. OFP3 overexpression also enhanced the phenotypes of BR‐deficient mutants, but largely suppressed those of BR‐enhanced plants. Moreover, treatment with either BR or bikinin, a GSK3‐like kinase inhibitor, induced OFP3 depletion, whereas GSK2 or brassinazole, a BR synthesis inhibitor, promoted OFP3 accumulation. Furthermore, OFP3 exhibited transcription repressor activity and was able to interact with itself as well as additional BR‐related components, including OFP1, OSH1, OSH15, OsBZR1, and GF14c. Importantly, GSK2 can phosphorylate OFP3 and enhance these interactions. We propose that OFP3, as a suppressor of both BR synthesis and signalling but stabilized by GSK2, incorporates into a transcription factor complex to facilitate BR signalling control, which is critical for the proper development of various tissues. Significance Statement: Brassinosteroid (BR) modulates various important agronomic traits in rice, but how the diverse hormone responses are integrated remains largely unclear. This study identified an OVATE family protein, OFP3, as a critical integrator of a BR signalling transcription factor complex, that interacts with a number of known components of BR signalling to suppress BR responses. As OFP3 forms the negative regulatory loops with BR signalling and biosynthesis, OFP3 could function as a stabilizer of BR signalling to moderate the signal magnitude.