Department of Biology, Centre for Forest Biology, University of Victoria, Victoria, BC V8P 5C2, Canada.
Department of Biochemistry, Max Planck Institute for Chemical Ecology, Jena 07745, Germany.
Plant Cell. 2022 Jul 30;34(8):2925-2947. doi: 10.1093/plcell/koac135.
Salicinoids are salicyl alcohol-containing phenolic glycosides with strong antiherbivore effects found only in poplars and willows. Their biosynthesis is poorly understood, but recently a UDP-dependent glycosyltransferase, UGT71L1, was shown to be required for salicinoid biosynthesis in poplar tissue cultures. UGT71L1 specifically glycosylates salicyl benzoate, a proposed salicinoid intermediate. Here, we analyzed transgenic CRISPR/Cas9-generated UGT71L1 knockout plants. Metabolomic analyses revealed substantial reductions in the major salicinoids, confirming the central role of the enzyme in salicinoid biosynthesis. Correspondingly, UGT71L1 knockouts were preferred to wild-type by white-marked tussock moth (Orgyia leucostigma) larvae in bioassays. Greenhouse-grown knockout plants showed substantial growth alterations, with decreased internode length and smaller serrated leaves. Reinserting a functional UGT71L1 gene in a transgenic rescue experiment demonstrated that these effects were due only to the loss of UGT71L1. The knockouts contained elevated salicylate (SA) and jasmonate (JA) concentrations, and also had enhanced expression of SA- and JA-related genes. SA is predicted to be released by UGT71L1 disruption, if salicyl salicylate is a pathway intermediate and UGT71L1 substrate. This idea was supported by showing that salicyl salicylate can be glucosylated by recombinant UGT71L1, providing a potential link of salicinoid metabolism to SA and growth impacts. Connecting this pathway with growth could imply that salicinoids are under additional evolutionary constraints beyond selective pressure by herbivores.
柳醇苷是一种仅存在于杨树和柳树中的含有水杨醇的酚糖苷，具有很强的抗食草动物作用。其生物合成知之甚少，但最近发现一个 UDP 依赖性糖基转移酶 UGT71L1，是杨树组织培养中柳醇苷生物合成所必需的。UGT71L1 特异性地糖基化水杨苯甲酸，一种被提议的柳醇苷中间体。在这里，我们分析了经 CRISPR/Cas9 产生的转基因 UGT71L1 敲除植物。代谢组学分析显示主要柳醇苷大量减少，证实了该酶在柳醇苷生物合成中的核心作用。相应地，在生物测定中，白纹卷蛾幼虫更喜欢 UGT71L1 敲除的植物，而不是野生型植物。温室种植的敲除植物表现出明显的生长变化，节间长度缩短，锯齿状叶片变小。在转基因拯救实验中重新插入一个功能性 UGT71L1 基因表明，这些影响仅归因于 UGT71L1 的缺失。敲除植物中含有较高浓度的水杨酸（SA）和茉莉酸（JA），并且 SA 和 JA 相关基因的表达也增强了。如果水杨基水杨酸是一种途径中间体和 UGT71L1 的底物，那么 SA 可能是由 UGT71L1 破坏释放的。这一想法得到了支持，表明水杨基水杨酸可以被重组 UGT71L1 糖基化，为柳醇苷代谢与 SA 和生长影响之间提供了潜在的联系。将该途径与生长联系起来可能意味着柳醇苷除了受到食草动物的选择性压力之外，还受到其他进化限制。
