Grain size and weight are important determinants of crop yield. Although the ubiquitin pathway has been implicated in the grain development in rice (Oryza sativa), the underlying genetic and molecular mechanisms remain largely unknown. Here, we report that the Plant U-box (PUB) E3 ubiquitin ligase OsPUB33 interferes with the OsNAC120-BG1 module to control rice grain development. Functional loss of OsPUB33 triggers elevated photosynthetic rates and greater sugar translocation, leading to enhanced cell proliferation and accelerated grain filling. These changes cause enlarged spikelet hulls, thereby increasing final grain size and weight. OsPUB33 interacts with transcription factor OsNAC120, resulting in its ubiquitination and degradation. Unlike OsPUB33, OsNAC120 promotes grain size and weight: OsNAC120-overexpression plants harbor large and heavy grains, whereas osnac120 loss-of-function mutants produce small grains. Genetic interaction analysis supports that OsPUB33 and OsNAC120 function at least partially in a common pathway to control grain development, but have opposite functions. Additionally, OsNAC120 transcriptionally activates BIG GRAIN1 (BG1), a prominent modulator of grain size, whereas OsPUB33 impairs the OsNAC120-mediated regulation of BG1. Collectively, our findings uncover an important molecular framework for the control of grain size and weight by the OsPUB33–OsNAC120–BG1 regulatory module and provide promising targets for improving crop yield.

中文翻译：

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E3 连接酶 OsPUB33 通过调节 OsNAC120-BG1 模块来控制水稻粒径和重量


谷物大小和重量是作物产量的重要决定因素。尽管泛素途径与水稻 （Oryza sativa） 的谷物发育有关，但潜在的遗传和分子机制在很大程度上仍然未知。在这里，我们报道了植物 U 盒 （PUB） E3 泛素连接酶 OsPUB33 干扰 OsNAC120-BG1 模块以控制水稻籽粒发育。OsPUB33 的功能丧失会触发光合速率升高和糖易位增加，导致细胞增殖增强和籽粒灌浆加速。这些变化导致小穗壳增大，从而增加最终的粒径和重量。OsPUB33 与转录因子 OsNAC120 相互作用，导致其泛素化和降解。与 OsPUB33 不同，OsNAC120 促进颗粒大小和重量：OsNAC120 过表达植物具有大而重的颗粒，而 OsNAC120 功能丧失突变体产生小颗粒。遗传相互作用分析支持 OsPUB33 和 OsNAC120 至少部分在控制籽粒发育的共同途径中发挥作用，但具有相反的功能。此外，OsNAC120 转录激活 BIG GRAIN1 （BG1），这是一种重要的粒径调节剂，而 OsPUB33 损害 OsNAC120 介导的 BG1 调节。总的来说，我们的研究结果揭示了通过 OsPUB33-OsNAC120-BG1 调节模块控制粒度和重量的重要分子框架，并为提高作物产量提供了有希望的目标。