Lignans are a major class of secondary metabolites distributed widely in the plant kingdom that are derived from coupling of phenylpropanoid (C6-C3) units. Most lignans are 8–8'-linked, and are often found in their glycosylated forms, which are catalyzed by UDP-dependent glycosyltransferase (UGT). Up to now, all UGTs involved in lignans biosynthesis are determined with substrate promiscuity. Here, IiUGT71B2 is reported from Isatis indigotica that specific catalyzes 4-O and 4′-O glycosylation of furan (lariciresinol) and dibenzylbutyrolactone (matairesinol) type lignans. Transcriptional profile of IiUGT71B2 indicates its involvement in lignan glycosides biosynthesis, which is co-expressed with other lignan biosynthetic genes, and is consistent with metabolic distribution of lignans in organs and tissues as well. Both in vitro and in vivo experiments demonstrate IiUGT71B2 catalyzes the mono- and di- glycosylation of lariciresinol and mono-glycosylation of matairesinol. The ligand docking and site-directed mutagenesis suggest Asn261, Ser289, Ala356, and Tyr395 as key residues, which may determine its catalytic efficiency together with the narrow binding pocket of IiUGT71B2. This study provides insights into lignan metabolism and functional diversity of plant UGTs.

木酚素是广泛分布于植物界的一类主要次级代谢产物，来源于苯丙素 (C6-C3) 单元的偶联。大多数木脂素是 8–8' 连接的，通常以糖基化形式存在，由 UDP 依赖性糖基转移酶 (UGT) 催化。到目前为止，所有参与木脂素生物合成的UGTs都是由底物混杂决定的。在这里，IiUGT71B2 来自板蓝根，它特异性催化呋喃（lariciresinol）和二苄基丁内酯（matairesinol）型木脂素的4- O和 4'- O糖基化。IiUGT71B2的转录谱表明其参与木脂素苷类生物合成，与其他木脂素生物合成基因共表达，也与木脂素在器官和组织中的代谢分布一致。体外和体内实验均证明 IiUGT71B2 催化落叶松素醇的单糖基化和二糖基化以及马泰素醇的单糖基化。配体对接和定点诱变表明 Asn261、Ser289、Ala356 和 Tyr395 是关键残基，这可能决定其催化效率以及 IiUGT71B2 的窄结合口袋。本研究提供了对植物 UGT 的木脂素代谢和功能多样性的见解。