Key Laboratory of Plant Resources/Beijing Botanical Garden, Institute of Botany, Chinese Academy of Sciences, Beijing, China.
University of Chinese Academy of Sciences, Beijing, China.
J Exp Bot. 2017 Jan 1;68(3):597-612. doi: 10.1093/jxb/erw420.
Flavonols are one of the largest groups of flavonoids that confer benefits for the health of plants and animals. Flavonol glycosides are the predominant flavonoids present in the model legume Lotus japonicus. The molecular mechanisms underlying the biosynthesis of flavonol glycosides as yet remain unknown in L. japonicus. In the present study, we identified a total of 188 UDP-glycosyltransferases (UGTs) in L. japonicus by genome-wide searching. Notably, 12 UGTs from the UGT72 family were distributed widely among L. japonicus chromosomes, expressed in all tissues, and showed different docking scores in an in silico bioinformatics docking analysis. Further enzymatic assays showed that five recombinant UGTs (UGT72AD1, UGT72AF1, UGT72AH1, UGT72V3, and UGT72Z2) exhibit activity toward flavonol, flavone, and isoflavone aglycones. In particular, UGT72AD1, UGT72AH1, and UGT72Z2 are flavonol-specific UGTs with different kinetic properties. In addition, the overexpression of UGT72AD1 and UGT72Z2 led to increased accumulation of flavonol rhamnosides in L. japonicus and Arabidopsis thaliana. Moreover, the increase of kaempferol 3-O-rhamnoside-7-O-rhamnoside in transgenic A. thaliana inhibited root growth as compared with the wild-type control. These results highlight the significance of the UGT72 family in flavonol glycosylation and the role of flavonol rhamnosides in plant growth.
类黄酮是黄酮类化合物中最大的一类，对动植物的健康有益。类黄酮糖苷是模式豆科植物百脉根中主要存在的类黄酮。类黄酮糖苷生物合成的分子机制在百脉根中尚不清楚。本研究通过全基因组搜索，在百脉根中鉴定了总共 188 个 UDP-糖基转移酶（UGT）。值得注意的是，UGT72 家族的 12 个 UGT 广泛分布于百脉根染色体上，在所有组织中表达，并在计算机生物信息学对接分析中显示出不同的对接分数。进一步的酶促分析表明，五种重组 UGT（UGT72AD1、UGT72AF1、UGT72AH1、UGT72V3 和 UGT72Z2）对类黄酮、黄酮和异黄酮苷元均具有活性。特别是 UGT72AD1、UGT72AH1 和 UGT72Z2 是具有不同动力学特性的类黄酮特异性 UGT。此外，UGT72AD1 和 UGT72Z2 的过表达导致百脉根和拟南芥中类黄酮鼠李糖苷的积累增加。此外，与野生型对照相比，转基因拟南芥中山奈酚 3-O-鼠李糖苷-7-O-鼠李糖苷的增加抑制了根的生长。这些结果突出了 UGT72 家族在类黄酮糖基化中的重要性以及类黄酮鼠李糖苷在植物生长中的作用。
