Description:
<p>Brassinosteroids (BRs) are a class of steroid hormones regulating multiple aspects of plant growth, development, and adaptation. Compared with extensive studies in Arabidopsis (<italic>Arabidopsis thaliana</italic>), the mechanism of BR signaling in rice (<italic>Oryza sativa</italic>) is less understood. Here, we identified OsWRKY53, a transcription factor involved in defense responses, as an important regulator of rice BR signaling. Phenotypic analyses showed that <italic>OsWRKY53</italic> overexpression led to enlarged leaf angles and increased grain size, in contrast to the erect leaves and smaller seeds in <italic>oswrky53</italic> mutant. In addition, the <italic>oswrky53</italic> exhibited decreased BR sensitivity, whereas <italic>OsWRKY53</italic> overexpression plants were hypersensitive to BR, suggesting that OsWRKY53 positively regulates rice BR signaling. Moreover, we show that OsWRKY53 can interact with and be phosphorylated by the OsMAPKK4-OsMAPK6 cascade, and the phosphorylation is required for the biological function of OsWRKY53 in regulating BR responses. Furthermore, we found that BR promotes OsWRKY53 protein accumulation but represses <italic>OsWRKY53</italic> transcript level. Taken together, this study revealed the novel role of OsWRKY53 as a regulator of rice BR signaling and also suggested a potential role of OsWRKY53 in mediating the cross talk between the hormone and other signaling pathways.</p>