Yin Qinggang, Shen Guoan, Di Shaokang, Fan Cunying, Chang Zhenzhan, Pang Yongzhen
The Key Laboratory of Plant Resources/Beijing Botanical Garden, Institute of Botany, the Chinese Academy of Sciences, Beijing 100093, China.
Key Laboratory of Plant Molecular and Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.
Plant Cell Physiol. 2017 Sep 1;58(9):1558-1572. doi: 10.1093/pcp/pcx081.
Flavonoids, natural products abundant in the model legume Glycine max, confer benefits to plants and to animal health. Flavonoids are present in soybean mainly as glycoconjugates. However, the mechanisms of biosynthesis of flavonoid glycosides are largely unknown in G. max. In the present study, 212 putative UDP-glycosyltransferase (UGT) genes were identified in G. max by genome-wide searching. The GmUGT genes were distributed differentially among the 20 chromosomes, and they were expressed in various tissues with distinct expression profiles. We further analyzed the enzymatic activities of 11 GmUGTs that are potentially involved in flavonoid glycosylation, and found that six of them (UGT72X4, UGT72Z3, UGT73C20, UGT88A13, UGT88E19 and UGT92G4) exhibited activity toward flavonol, isoflavone, flavone and flavanol aglycones with different kinetic properties. Among them, UGT72X4, UGT72Z3 and UGT92G4 are flavonol-specific UGTs, and UGT73C20 and UGT88E19 exhibited activity toward both flavonol and isoflavone aglycones. In particular, UGT88A13 exhibited activity toward epicatechin, but not for the flavonol aglycones kaempferol and quercetin. Overexpression of these six GmUGT genes significantly increased the contents of isoflavone and flavonol glucosides in soybean hairy roots. In addition, overexpression of these six GmUGT genes also affected flavonol glycoside contents differently in seedlings and seeds of transgenic Arabidopsis thaliana. We provide valuable information on the identification of all UGT genes in soybean, and candidate GmUGT genes for potential metabolic engineering of flavonoid compounds in both Escherichia coli and plants.
黄酮类化合物是模式豆科植物大豆中丰富的天然产物，对植物和动物健康都有益处。黄酮类化合物在大豆中主要以糖缀合物的形式存在。然而，大豆中黄酮糖苷的生物合成机制在很大程度上尚不清楚。在本研究中，通过全基因组搜索在大豆中鉴定出212个假定的尿苷二磷酸糖基转移酶（UGT）基因。GmUGT基因在20条染色体上分布不同，且在各种组织中表达，具有不同的表达谱。我们进一步分析了11个可能参与黄酮糖基化的GmUGT的酶活性，发现其中6个（UGT72X4、UGT72Z3、UGT73C20、UGT88A13、UGT88E19和UGT92G4）对黄酮醇、异黄酮、黄酮和黄烷醇苷元表现出活性，且具有不同的动力学特性。其中，UGT72X4、UGT72Z3和UGT92G4是黄酮醇特异性UGT，UGT73C20和UGT88E19对黄酮醇和异黄酮苷元均表现出活性。特别是，UGT88A13对表儿茶素表现出活性，但对黄酮醇苷元山奈酚和槲皮素无活性。这6个GmUGT基因的过表达显著增加了大豆毛状根中异黄酮和黄酮醇糖苷的含量。此外，这6个GmUGT基因的过表达对转基因拟南芥幼苗和种子中黄酮醇糖苷含量的影响也不同。我们提供了关于大豆中所有UGT基因鉴定的有价值信息，以及用于大肠杆菌和植物中黄酮类化合物潜在代谢工程的候选GmUGT基因。
