Achnine Lahoucine, Huhman David V, Farag Mohamed A, Sumner Lloyd W, Blount Jack W, Dixon Richard A
Plant Biology Division, Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK 73401, USA.
Plant J. 2005 Mar;41(6):875-87. doi: 10.1111/j.1365-313X.2005.02344.x.
The biosynthesis of triterpene saponins is poorly characterized in spite of the importance of these glycosylated secondary metabolites for plant defense and animal health. The model legume Medicago truncatula synthesizes more than 30 different saponins based on at least five triterpene aglycones; soyasapogenols B and E, medicagenic acid, hederagenin and bayogenin. We have employed an inducible cell culture system, DNA array-based and in silico transcript profiling, and targeted metabolite profiling, to identify triterpene glycosyltransferases (GTs) from among the more than 300 GTs expressed in M. truncatula. Two uridine diphosphate glucosyltransferases were functionally characterized; UGT73K1 with specificity for hederagenin and soyasapogenols B and E, and UGT71G1 with specificity for medicagenic acid. The latter enzyme also glycosylated certain isoflavones and the flavonol quercetin with higher efficiency than triterpenes; however, integrated transcript and metabolite profiling supported a function for UGT71G1 in terpenoid but not (iso)flavonoid biosynthesis in the elicited cell cultures.
尽管这些糖基化次生代谢产物对植物防御和动物健康具有重要意义，但三萜皂苷的生物合成仍未得到充分表征。模式豆科植物蒺藜苜蓿基于至少五种三萜苷元合成了30多种不同的皂苷；大豆皂苷元B和E、苜蓿酸、常春藤皂苷元及蔷薇酸。我们利用诱导性细胞培养系统、基于DNA阵列和计算机模拟的转录谱分析以及靶向代谢物谱分析，从蒺藜苜蓿中表达的300多种糖基转移酶（GTs）中鉴定出三萜糖基转移酶。对两种尿苷二磷酸葡萄糖基转移酶进行了功能表征；UGT73K1对常春藤皂苷元和大豆皂苷元B及E具有特异性，UGT71G1对苜蓿酸具有特异性。后一种酶对某些异黄酮和黄酮醇槲皮素的糖基化效率也高于三萜；然而，整合的转录和代谢物谱分析支持UGT71G1在诱导的细胞培养物中参与萜类而非（异）黄酮类生物合成的功能。
