Riboflavin is the precursor of essential cofactors for diverse metabolic processes. Unlike animals, plants can de novo produce riboflavin through an ancestrally conserved pathway, like bacteria and fungi. However, the mechanism by which riboflavin regulates seed development is poorly understood. Here, we report a novel maize (Zea mays L.) opaque mutant o18, which displays an increase in lysine accumulation, but impaired endosperm filling and embryo development. O18 encodes a rate-limiting bifunctional enzyme ZmRIBA1, targeted to plastid where to initiate riboflavin biosynthesis. Loss of function of O18 specifically disrupts respiratory complexes I and II, but also decreases SDH1 flavinylation, and in turn shifts the mitochondrial tricarboxylic acid (TCA) cycle to glycolysis. The deprivation of cellular energy leads to cell-cycle arrest at G1 and S phases in both mitosis and endoreduplication during endosperm development. The unexpected up-regulation of cell-cycle genes in o18 correlates with the increase of H3K4me3 levels, revealing a possible H3K4me-mediated epigenetic back-up mechanism for cell-cycle progression under unfavourable circumstances. Overexpression of O18 increases riboflavin production and confers osmotic tolerance. Altogether, our results substantiate a key role of riboflavin in coordinating cellular energy and cell cycle to modulate maize endosperm development.

中文翻译：

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核黄素整合细胞能量学和细胞周期调控玉米种子发育

核黄素是多种代谢过程必需辅因子的前体。与动物不同，植物可以像细菌和真菌一样通过祖先保守的途径从头产生核黄素。然而，人们对核黄素调节种子发育的机制知之甚少。在这里，我们报告了一种新型玉米 ( Zea mays L.) 不透明突变体o18，该突变体显示赖氨酸积累增加，但胚乳充盈和胚胎发育受损。O18编码一种限速双功能酶 ZmRIBA1，靶向质体以启动核黄素生物合成。O18功能丧失特异性破坏呼吸复合物 I 和 II，但也会降低 SDH1 黄素化，进而将线粒体三羧酸 (TCA) 循环转变为糖酵解。在胚乳发育过程中，细胞能量的剥夺导致细胞周期停滞在有丝分裂和核内复制的 G1 和 S 期。o18中细胞周期基因的意外上调与 H3K4me3 水平的增加相关，揭示了 H3K4me 介导的可能在不利情况下细胞周期进展的表观遗传备份机制。O18的过表达增加核黄素的产生并赋予渗透耐受性。总之，我们的结果证实了核黄素在协调细胞能量和细胞周期以调节玉米胚乳发育中的关键作用。