Brassinosteroid Regulates 3‑Hydroxy-3-methylglutaryl CoA Reductase to Promote Grape Fruit Development

Brassinosteroids (BRs) are known to regulate plant growth and development. However, only little is known about their mechanism in the regulation of berry development in grapes. This study demonstrates that BR treatment enhances the accumulation of fruit sugar components, reduces the content of organic acids (e.g., tartaric acid), promotes coloration, and increases the anthocyanin content in grape berries at the onset of the veraison, half veraison, and full veraison stages at the rate of 0.0998, 0.0560, and 0.0281 mg·g–1, respectively. In addition, BR treatment was also found to accelerate the biosynthesis of terpenoid aroma components, such as α-pinene, d-limonene, and γ-terpinene, which influence the aromatic composition of grapes. BRs can negatively regulate the expression of VvHMGR, a key gene involved in the mevalonate (MVA) pathway, and reduce the activity of 3-hydroxy-3-methylglutaryl CoA reductase (HMGR). Inhibiting the expression of HMGR promoted the accumulation of anthocyanins and fruit coloration. Meanwhile, after the inhibition, the contents of auxin indole-3-acetic acid (IAA), abscisic acid (ABA), and brassinosteroid (BR) increased, while gibberellin (GA3) and zeatin riboside (ZR) decreased, and its aromatic composition also changed. Therefore, it may be concluded that BRs inhibited HMGR activity and cooperated with VvHMGR to regulate the formation of color, aroma, and other quality characteristics in fruits.油菜素甾醇（Brassinosteroids，BRs）已知可调控植物生长发育。然而，目前对其调控葡萄浆果发育的机制仍知之甚少。本研究表明，BR处理可提升葡萄浆果在转色初期、半转色期及全转色期的果实糖组分积累量，降低有机酸（如酒石酸）含量，促进果实着色，并分别以0.0998、0.0560及0.0281 mg·g–1的水平增加浆果内花青素含量。 此外，研究发现BR处理可加速萜类香气组分的生物合成，包括α-蒎烯、d-柠檬烯及γ-松油烯，这些组分可影响葡萄的香气组成。BRs可负调控甲羟戊酸（MVA）途径的关键基因VvHMGR的表达，并降低3-羟基-3-甲基戊二酰辅酶A还原酶（HMGR）的活性。抑制HMGR的表达可促进花青素积累与果实着色。同时，抑制HMGR表达后，生长素吲哚-3-乙酸（IAA）、脱落酸（ABA）及BR的含量均有所上升，而赤霉素（GA3）与玉米素核苷（ZR）的含量则下降，果实香气组成亦发生改变。 因此可推断，BRs通过抑制HMGR活性并协同VvHMGR调控果实着色、香气及其他品质性状的形成。