Brassinosteroids (BRs) play essential roles in regulating plant growth and development, however, gaps still remain in our understanding of the BR signaling network. We previously cloned a grain length quantitative trait locus qGL3, encoding a rice (Oryza sativa L.) protein phosphatase with Kelch-like repeat domain (OsPPKL1), that negatively regulates grain length and BR signaling. To further explore the BR signaling network, we performed phosphoproteomic analysis to screen qGL3-regulated downstream components. We selected a 14-3-3 protein OsGF14b from the phosphoproteomic data for further analysis. qGL3 promoted the phosphorylation of OsGF14b and induced the interaction intensity between OsGF14b and OsBZR1. In addition, phosphorylation of OsGF14b played an important role in regulating nucleocytoplasmic shuttling of OsBZR1. The serine acids (Ser258Ser259) residues of OsGF14b play an essential role in BR-mediated responses and plant development. Genetic and molecular analyses indicated that OsGF14b functions as a negative regulator in BR signaling and represses the transcriptional activation activity of OsBZR1. Collectively, these results demonstrate that qGL3 induces the phosphorylation of OsGF14b, which modulates nucleocytoplasmic shuttling and transcriptional activation activity of OsBZR1, to eventually negatively regulate BR signaling and grain length in rice.

中文翻译：

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qGL3/OsPPKL1 诱导 14-3-3 蛋白 OsGF14b 磷酸化，抑制油菜素类固醇信号传导中的 OsBZR1 功能

油菜素类固醇（BR）在调节植物生长和发育中发挥着重要作用，然而，我们对 BR 信号网络的理解仍然存在差距。我们之前克隆了一个粒长数量性状基因座 qGL3，编码具有 Kelch 样重复结构域 (OsPPKL1) 的水稻 (Oryza sativa L.) 蛋白磷酸酶，该酶负向调节粒长和 BR 信号传导。为了进一步探索 BR 信号网络，我们进行了磷酸化蛋白质组学分析来筛选 qGL3 调节的下游组件。我们从磷酸化蛋白质组数据中选择了 14-3-3 蛋白 OsGF14b 进行进一步分析。qGL3促进OsGF14b的磷酸化并诱导OsGF14b和OsBZR1之间的相互作用强度。此外，OsGF14b 的磷酸化在调节 OsBZR1 的核质穿梭中发挥着重要作用。OsGF14b 的丝氨酸 (Ser258Ser259) 残基在 BR 介导的反应和植物发育中发挥重要作用。遗传和分子分析表明，OsGF14b 在 BR 信号传导中充当负调节因子，并抑制 OsBZR1 的转录激活活性。总的来说，这些结果表明 qGL3 诱导 OsGF14b 磷酸化，从而调节 OsBZR1 的核质穿梭和转录激活活性，最终负向调节水稻中的 BR 信号传导和籽粒长度。