日前，国际主流刊物《PLoS Genetics》 在线发表了中科院遗传与发育生物学研究所和中国水稻研究所合作的最新研究成果。这篇题为“The U-Box E3 Ubiquitin Ligase TUD1 Functions with a Heterotrimeric G α Subunit to Regulate Brassinosteroid-Mediated Growth in Rice”的论文(DOI:10.1371/journal.pgen.1003391)揭示了一个新的水稻BR不敏感矮秆突变体—taihu dwarf1(tud1)。胡兴明博士为论文的第一作者。

虽然异三聚体鸟嘌呤核苷结合蛋白（简称G蛋白）复合体是真核细胞中保守的一类重要信号转导分子,但是它们在植物如何发挥作用的分子机制有待阐明。前期研究结果表明水稻G蛋白α亚基RGA1（D1）参与了油菜素内酯（BR）介导的信号响应途径，但是究竟D1如何介导BR信号转导的分子机制并不清楚。

研究人员发现了一个新的水稻BR不敏感矮秆突变体—taihu dwarf1(tud1)。该突变体是由于一个编码U-box E3泛素连接酶的基因突变所造成。详细的分析表明tud1突变会导致水稻第二节间细胞纵向细胞层排列紊乱和外颖中薄壁细胞体积变小，并且D1可以通过与TUD1直接相互作用来介导BR信号响应通路。该研究结果揭示了D1和TUD1共同作用介导了一条新的BR信号响应通路。进一步的研究发现TUD1在植物中具有保守性，为进一步提高水稻等作物产量提供了新的途径。

论文摘要：

Heterotrimeric G proteins are an important group of signaling molecules found in eukaryotes. They function with G-protein-coupled-receptors (GPCRs) to transduce various signals such as steroid hormones in animals. Nevertheless, their functions in plants are not well-defined. Previous studies suggested that the heterotrimeric G protein α subunit known as D1/RGA1 in rice is involved in a phytohormone gibberellin-mediated signaling pathway. Evidence also implicates D1 in the action of a second phytohormone Brassinosteroid (BR) and its pathway. However, it is unclear how D1 functions in this pathway, because so far no partner has been identified to act with D1. In this study, we report a D1 genetic interactor Taihu Dwarf1 (TUD1) that encodes a functional U-box E3 ubiquitin ligase. Genetic, phenotypic, and physiological analyses have shown that tud1 is epistatic to d1 and is less sensitive to BR treatment. Histological observations showed that the dwarf phenotype of tud1 is mainly due to decreased cell proliferation and disorganized cell files in aerial organs. Furthermore, we found that D1 directly interacts with TUD1. Taken together, these results demonstrate that D1 and TUD1 act together to mediate a BR-signaling pathway. This supports the idea that a D1-mediated BR signaling pathway occurs in rice to affect plant growth and development.

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