Flavonol glycosides are health-promoting phytochemicals important for human nutrition and plant defence against environmental stresses. Glycosylation modification greatly enriches the diversity of flavonols. Morella rubra, a member of the Myricaceae, contains high amount of myricetin 3-O-rhamnoside (M3Rha), quercetin 3-O-rhamnoside (Q3Rha), and quercetin 3-O-galactoside (Q3Gal). In the present study, MrUGT78R1 and MrUGT78R2 were identified as two functional UDP-rhamnosyltransferases, while MrUGT78W1 was identified as a UDP-galactosyltransferase. Site-directed mutagenesis identified Pro143 and Asn386 as important residues for rhamnosyl transfer activity of MrUGT78R1 while these two corresponding positions in MrUGT78W1 (i.e. Ser147 and Asn370) also play important role for galactosyl transfer activity. Transient expression data for these three MrUGTs in Nicotiana benthamiana tested the function of MrUGT78R1 and MrUGT78R2 as rhamnosyltransferases and MrUGT78W1 as a galactosyltransferase in glycosylation of flavonols. This work enriches the diversity of UDP-rhamnosyltransferase in planta and identifies two amino acid positions important for both rhamnosyltransferase and galactosyltransferase.

中文翻译：

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红色莫雷拉黄酮醇糖基化中 UDP-鼠李糖基转移酶和 UDP-半乳糖基转移酶的鉴定

黄酮醇苷是促进健康的植物化学物质，对人类营养和植物抵御环境压力很重要。糖基化修饰极大地丰富了黄酮醇的多样性。Morella rubra 是杨梅科的成员，含有大量的杨梅素 3-O-鼠李糖苷 (M3Rha)、槲皮素 3-O-鼠李糖苷 (Q3Rha) 和槲皮素 3-O-半乳糖苷 (Q3Gal)。在本研究中，MrUGT78R1 和MrUGT78R2 被鉴定为两个功能性UDP-鼠李糖基转移酶，而MrUGT78W1 被鉴定为UDP-半乳糖基转移酶。定点诱变将Pro143 和Asn386 鉴定为MrUGT78R1 鼠李糖基转移活性的重要残基，而MrUGT78W1 中的这两个相应位置（即Ser147 和Asn370）也对半乳糖基转移活性起重要作用。这三种 MrUGT 在本氏烟草中的瞬时表达数据测试了 MrUGT78R1 和 MrUGT78R2 作为鼠李糖基转移酶和 MrUGT78W1 作为半乳糖基转移酶在黄酮醇糖基化中的功能。这项工作丰富了植物中 UDP-鼠李糖基转移酶的多样性，并确定了两个对鼠李糖基转移酶和半乳糖基转移酶都很重要的氨基酸位置。