Increasing grain yield is a major goal of breeders due to the rising global demand for food. We previously reported that the miR397–LACCASE (OsLAC) module regulates brassinosteroid (BR) signaling and grain yield in rice (Oryza sativa). However, the precise roles of laccase enzymes in the BR pathway remain unclear. Here, we report that OsLAC controls grain yield by preventing the turnover of TRANSTHYRETIN-LIKE (OsTTL), a negative regulator of BR signaling. Overexpressing OsTTL decreased BR sensitivity in rice, while loss-of-function of OsTTL led to enhanced BR signaling and increased grain yield. OsLAC directly binds to OsTTL and regulates its phosphorylation-mediated turnover. The phosphorylation site Ser226 of OsTTL is essential for its ubiquitination and degradation. Overexpressing the dephosphorylation-mimic form of OsTTL (OsTTLS226A) resulted in more severe defects than did overexpressing OsTTL. These findings provide insight into the role of an ancient laccase in BR signaling and suggest that the OsLAC–OsTTL module could serve as a target for improving grain yield.

中文翻译：

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转甲状腺素蛋白样蛋白作用于 miR397 和 LACCASE 下游，调节水稻籽粒产量

由于全球粮食需求不断增长，提高粮食产量是育种者的主要目标。我们之前报道过 miR397-LACCASE (OsLAC) 模块调节油菜素类固醇 (BR) 信号传导和水稻 (Oryza sativa) 的籽粒产量。然而，漆酶在 BR 途径中的确切作用仍不清楚。在这里，我们报道了 OsLAC 通过阻止转甲状腺素蛋白样 (OsTTL) 的周转来控制谷物产量，TRANSTHYRETIN-LIKE 是 BR 信号传导的负调节因子。过度表达 OsTTL 会降低水稻的 BR 敏感性，而 OsTTL 功能丧失则导致 BR 信号增强并增加谷物产量。 OsLAC 直接与 OsTTL 结合并调节其磷酸化介导的周转。 OsTTL 的磷酸化位点 Ser226 对于其泛素化和降解至关重要。过度表达 OsTTL 的去磷酸化模拟形式 (OsTTLS226A) 比过度表达 OsTTL 会导致更严重的缺陷。这些发现深入了解了古老漆酶在 BR 信号传导中的作用，并表明 OsLAC-OsTTL 模块可以作为提高谷物产量的目标。