CYP93G2 Is a Flavanone 2-Hydroxylase Required for C-Glycosylflavone Biosynthesis in Rice
CYP93G2 Is a Flavanone 2-Hydroxylase Required for C-Glycosylflavone Biosynthesis in Rice
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DOI：
10.1104/pp.110.161042
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发表时间：
2010-09-01
期刊：
影响因子：
7.4
通讯作者：
Lo, Clive
中科院分区：
文献类型：
--
作者：
Du, Yegang;Chu, Hung;Lo, Clive
C-糖基黄酮在植物界中普遍存在，其中许多对人类健康具有有益作用。它们是一类特殊的类黄酮糖苷，其中糖与黄酮骨架C-连接。长期以来，人们一直认为C-糖基黄酮具有与O-糖基黄酮不同的生物合成来源。在水稻（Oryza sativa）中，最近描述了接受2-羟基黄烷酮底物的C-葡糖基转移酶（OsCGT）和选择性地将C-葡糖基-2-羟基黄烷酮转化为6C-葡糖基黄酮的脱氢酶活性。在本研究中，我们提供了在体外和在植物中的证据，水稻P450 CYP 93 G2蛋白编码的Os 06 g 01250是一个功能性的黄烷酮2-羟化酶。CYP 93 G2与CYP 93 B亚家族相关，该亚家族由双子叶植物黄酮合酶II酶组成。在NADPH存在下，重组CYP 93 G2将柚皮素和圣草酚转化为相应的2-羟基黄烷酮。此外，CYP 93 G2产生2-羟基黄烷酮，其在转基因拟南芥（Arabidopsis thaliana）中通过O-糖基化修饰。CYP 93 G2和OsCGT在拟南芥中的共表达导致了二苯甲酰甲烷互变异构形式的C-葡萄糖基-2-羟基黄烷酮的产生。先前报道了体外OsCGT反应产物的相同结构。因此，CYP 93 G2从黄烷酮产生2-羟基黄烷酮底物，用于在植物中通过OsCGT进行C-葡糖基化。此外，敲除水稻Os 06 g 01250（O.青粳稻“中华11”）优先消耗C-糖基化的芹菜素、C-糖基化的木犀草素和C-糖基化的黄菊醇的积累，但不影响麦黄酮的水平，麦黄酮通常作为0-糖苷存在于谷物中。综上所述，我们的工作最终指定CYP 93 G2作为第一个酶通道的黄烷酮C-糖基黄酮生物合成在水稻。
C-Glycosylflavones are ubiquitous in the plant kingdom, and many of them have beneficial effects on human health. They are a special group of flavonoid glycosides in which the sugars are C-linked to the flavone skeleton. It has been long presumed that C-glycosylflavones have a different biosynthetic origin from O-glycosylflavonoids. In rice (Oryza sativa), a C-glucosyltransferase (OsCGT) that accepts 2-hydroxyflavanone substrates and a dehydratase activity that selectively converts C-glucosyl-2-hydroxyflavanones to 6C-glucosylflavones were recently described. In this study, we provide in vitro and in planta evidence that the rice P450 CYP93G2 protein encoded by Os06g01250 is a functional flavanone 2-hydroxylase. CYP93G2 is related to the CYP93B subfamily, which consists of dicot flavone synthase II enzymes. In the presence of NADPH, recombinant CYP93G2 converts naringenin and eriodictyol to the corresponding 2-hydroxyflavanones. In addition, CYP93G2 generates 2-hydroxyflavanones, which are modified by O-glycosylation in transgenic Arabidopsis (Arabidopsis thaliana). Coexpression of CYP93G2 and OsCGT in Arabidopsis resulted in the production of C-glucosyl-2-hydroxyflavanones in the dibenzoylmethane tautomeric form. The same structure was reported previously for the in vitro OsCGT reaction products. Thus, CYP93G2 generates 2-hydroxyflavanone substrates from flavanones for C-glucosylation by OsCGT in planta. Furthermore, knocking down Os06g01250 in rice (O. sativa subsp. japonica 'Zhonghua 11') preferentially depleted the accumulation of C-glycosylapigenin, C-glycosylluteolin, and C-glycosylchrysoeriol but did not affect the levels of tricin, which is frequently present as O-glycosides in cereals. Taken together, our work conclusively assigned CYP93G2 as the first enzyme that channels flavanones to C-glycosylflavone biosynthesis in rice.