Cit1,2RhaT and two novel CitdGlcTs participate in flavor-related flavonoid metabolism during citrus fruit development
Cit1,2RhaT and two novel CitdGlcTs participate in flavor-related flavonoid metabolism during citrus fruit development
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DOI：
10.1093/jxb/erz081
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发表时间：
2019-05-01
影响因子：
6.9
通讯作者：
Xu, Juan
中科院分区：
文献类型：
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作者：
Chen, Jiajing;Yuan, Ziyu;Xu, Juan
新橙皮糖苷是存在于某些黄酮类化合物中的二糖，给人一种苦味，这会显著影响柑橘类水果的商业价值。在本研究中，我们在柑橘基因组中发现了三个与1，2-鼠李糖基转移酶(1，2RhaT)密切相关的黄酮类-7-O-二葡萄糖基转移酶(DGlcT)基因。然而，50份材料的关联分析和柑橘×三叶胡椒F-1群体的共分离分析表明，只有1，2RhaT与新橙皮苷的积累有直接关联。在转基因烟草BY-2细胞中，CitdGlcts的过表达导致黄酮类-7-O-葡萄糖苷被催化生成无苦味的黄酮类-7-O-二葡萄糖苷，而Cit1，2RhaT的过表达则将同一底物转化为苦味的黄酮类-7-O-新橙皮糖苷。与1，2RhaT不同，在柑橘果实发育过程中，dGlcT与编码类黄酮生物合成限速酶CHS和CHI的表达模式相反。DGlcts和底物的非偶联作用可能导致黄酮类-7-O-二葡萄糖苷在大果柚果实中的微量积累。过去人类对1，2RhaT的缺失和功能突变的选择已经一步步导致了柑橘中与风味相关的代谢网络的进化。我们的研究为通过敲除1，2RhaT或通过遗传转化增强dGlcT的表达来操纵网络来改善柑橘果实的口感提供了潜在的基础。
Neohesperidosides are disaccharides that are present in some flavonoids and impart a bitter taste, which can significantly affect the commercial value of citrus fruits. In this study, we identified three flavonoid-7-O-di-glucosyltransferase (dGlcT) genes closely related to 1,2-rhamnosyltransferase (1,2RhaT) in citrus genomes. However, only 1,2RhaT was directly linked to the accumulation of neohesperidoside, as demonstrated by association analysis of 50 accessions and co-segregation analysis of an F-1 population derived from Citrus reticulata x Poncirus trifoliata. In transgenic tobacco BY2 cells, over-expression of CitdGlcTs resulted in flavonoid-7-O-glucosides being catalysed into bitterless flavonoid-7-O-di-glucosides, whereas over-expression of Cit1,2RhaT converted the same substrate into bitter-tasting flavonoid-7-O-neohesperidoside. Unlike 1,2RhaT, during citrus fruit development the dGlcTs showed an opposite expression pattern to CHS and CHI, two genes encoding rate-limiting enzymes of flavonoid biosynthesis. An uncoupled availability of dGlcTs and substrates might result in trace accumulation of flavonoid-7-O-di-glucosides in the fruit of C. maxima (pummelo). Past human selection of the deletion and functional mutation of 1,2RhaT has led step-by-step to the evolution of the flavor-related metabolic network in citrus. Our research provides the basis for potentially improving the taste in citrus fruit through manipulation of the network by knocking-out 1,2RhaT or by enhancing the expression of dGlcT using genetic transformation.