Li Weiyan, Zhang Jingjing, Zhang Wan, Zhang Qiuxin, Wang Haoyuan, Xu Tingting, Chen Zhongxian, Zhang Zemin
State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, Guangdong Provincial Key Laboratory of Plant Molecular Breeding, South China Agricultural University, Guang-zhou, 510642, China.
Plant J. 2025 Mar;121(6):e70105. doi: 10.1111/tpj.70105.
Flavonoids are secondary metabolites of plants that play various roles in plants. The transcriptional level regulation of flavonoid synthesis in plants has been extensively studied, but research on the protein level of flavonoid synthesis in plants is still limited. In the present study, a brown hull mutant, bh2, was screened from an ethane methyl sulfonate (EMS)-induced bank from the seeds of the indica cultivar RH2B. The bh2 mutant exhibited a brown hull phenotype and higher levels of total flavonoids and anthocyanins compared with wild-type plants. We identified the gene INHIBITOR FOR BROWN FURROWS 1 (IBF1) in the bh2 mutant through MutMap analysis and subsequently cloned it. IBF1 encodes an F-box protein and is involved in the formation of an SCF (S-phase kinase-associated protein 1 [SKP1], Cullin, and F-box) complex with the Oryza sativa SKP1-like proteins OSK1/OSK20. Through yeast two-hybrid, bimolecular fluorescence complementation, and pull-down assays, the interaction of IBF1 with chalcone synthase 1 (CHS1) was confirmed. This interaction facilitated the degradation of CHS1 through the ubiquitin-26S proteasome system. The ibf1 chs1 double mutants exhibited normal hull color, restoring the phenotype of ibf1. Genetic analysis suggested that IBF1 regulates hull color in a CHS1-dependent manner. Collectively, our study suggests that IBF1 serves as a crucial negative regulator that controls flavonoid biosynthesis by mediating CHS1 degradation, thereby regulating hull color.
类黄酮是植物的次生代谢产物，在植物中发挥着多种作用。植物中类黄酮合成的转录水平调控已得到广泛研究，但关于植物类黄酮合成蛋白质水平的研究仍然有限。在本研究中，从籼稻品种RH2B种子的甲基磺酸乙酯（EMS）诱变库中筛选出一个褐色颖壳突变体bh2。与野生型植株相比，bh2突变体表现出褐色颖壳表型以及更高水平的总黄酮和花青素。我们通过MutMap分析在bh2突变体中鉴定出基因INHIBITOR FOR BROWN FURROWS 1（IBF1），随后对其进行了克隆。IBF1编码一种F-box蛋白，并与水稻SKP1样蛋白OSK1/OSK20形成SCF（S期激酶相关蛋白1 [SKP1]、Cullin和F-box）复合体。通过酵母双杂交、双分子荧光互补和下拉实验，证实了IBF1与查尔酮合酶1（CHS1）的相互作用。这种相互作用通过泛素-26S蛋白酶体系统促进了CHS1的降解。ibf1 chs1双突变体表现出正常的颖壳颜色，恢复了ibf1的表型。遗传分析表明，IBF1以CHS1依赖的方式调控颖壳颜色。总的来说，我们的研究表明，IBF1作为一个关键的负调控因子，通过介导CHS1的降解来控制类黄酮生物合成，从而调控颖壳颜色。
