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Os BZR 1 turnover mediated by Os SK 22‐regulated U‐box E3 ligase Os PUB 24 in rice BR response
Author(s) -
Min Hye Jo,
Cui Li Hua,
Oh Tae Rin,
Kim Jong Hum,
Kim TaeWuk,
Kim Woo Taek
Publication year - 2019
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/tpj.14332
Subject(s) - chemistry
Summary Oryza sativa BRASSINAZOLE RESISTANT 1 (Os BZR 1) is the closest rice homolog of the Arabidopsis BZR 1 and bri1 ‐ EMS ‐ SUPPRESSOR 1 ( BES 1)/ BZR 2 transcription factors. Os BZR 1 plays a central role in the rice brassinosteroid signaling pathway. Despite its functional importance, the control mechanism by which the cellular stability of Os BZR 1 is regulated has not yet been fully elucidated. Here, we report that a rice U‐box E3 ubiquitin (Ub) ligase Os PUB 24 acts as a negative regulator in the BR signaling pathway via the 26S proteasome‐dependent degradation of Os BZR 1. The ospub24 T‐ DNA knock‐out mutant and Ubi: RNA i‐Os PUB 24 knock‐down rice plants displayed enhanced seedling growth, increased lamina joint bending, and hypersensitivity to brassinolide ( BL ). The expressions of the BR biosynthetic genes suppressed by BR in a negative feedback loop were lower in the mutant progeny than in the wild‐type rice plants, which indicated increased BR responses in the mutant line. Os PUB 24 ubiquitinated Os BZR 1, resulting in the proteasomal degradation of Os BZR 1. In addition, the stability of Os PUB 24 was downregulated by BL and bikinin, an inhibitor of Oryza sativa Shaggy/ GSK 3‐like kinase 22 (Os SK 22). Os SK 22, the homolog of Arabidopsis BRASSINOSTEROID INSENSITIVE 2 ( BIN 2) protein kinase, phosphorylated Os PUB 24 and elevated the cellular stability of Os PUB 24. Our findings suggest that Os PUB 24 participates in Os BZR 1 turnover, and that the regulatory networks of Os PUB 24, Os SK 22 and Os BZR 1 are crucial for fine‐tuning the BR response in rice.