Department for Biochemistry, Max Planck Institute for Chemical Ecology , Jena , Germany.
Plant Signal Behav. 2019;14(11):1668233. doi: 10.1080/15592324.2019.1668233. Epub 2019 Sep 18.
In response to herbivory, poplar produces among other compounds the volatile alcohol 2-phenylethanol and its corresponding glucoside 2-phenylethyl-β-D-glucopyranoside. While the free alcohol is released only upon herbivory, the glucoside accumulates also in undamaged leaves, but increases after herbivore feeding. Recently we showed that 2-phenylethanol and its glucoside are biosynthesized via separate pathways in . The phenylacetaldehyde synthase PtAAS1 plays a central role in the formation of herbivory-induced volatile 2-phenylethanol, while the phenylalanine decarboxylase PtAADC1 initiates a pathway responsible for the herbivory-induced production of 2-phenylethyl-β-D-glucopyranoside. Besides PtAAS1, possesses another aromatic aldehyde synthase PtAAS2 with enzymatic activity comparable to that of PtAAS1. However, in contrast to , which is exclusively expressed in herbivory-damaged leaves, was found to be expressed at constant levels in both damaged and undamaged leaves. Thus it has been hypothesized that PtAAS2 provides phenylacetaldehyde as substrate for the constitutive formation of 2-phenylethyl-β-D-glucopyranoside in undamaged trees. By generating RNAi-mediated knockdown plants, we show here that despite the similar activities of PtAAS1 and PtAAS2 , the latter enzyme does not contribute to the biosynthesis of 2-phenylethyl-β-D-glucopyranoside . Based on the recent finding that phenylpyruvic acid accumulates in undamaged poplar leaves, the constitutive formation of the glucoside may now be suggested to proceed via the Ehrlich pathway, which begins with the conversion of phenylalanine into phenylpyruvic acid.
针对食草性，杨树会产生包括挥发性醇 2-苯乙醇及其相应的葡萄糖苷 2-苯乙基-β-D-吡喃葡萄糖苷在内的多种化合物。虽然游离醇仅在受到食草性攻击时释放，但糖苷也会在未受损的叶片中积累，但在食草动物进食后会增加。最近我们表明，2-苯乙醇及其糖苷是通过 中的独立途径生物合成的。苯乙醛合酶 PtAAS1 在形成食草性诱导的挥发性 2-苯乙醇中起着核心作用，而苯丙氨酸脱羧酶 PtAADC1 则启动了一条负责食草性诱导产生 2-苯乙基-β-D-吡喃葡萄糖苷的途径。除了 PtAAS1， 还拥有另一种芳香醛合酶 PtAAS2，其酶活性与 PtAAS1 相当。然而，与仅在受到食草性损伤的叶片中表达的 不同， 在受损和未受损的叶片中均以恒定水平表达。因此，人们假设 PtAAS2 为未受损的 树木中 2-苯乙基-β-D-吡喃葡萄糖苷的组成形成提供苯乙醛作为底物。通过生成 RNAi 介导的 敲低植物，我们在这里表明，尽管 PtAAS1 和 PtAAS2 的活性相似，但后一种酶并不有助于 2-苯乙基-β-D-吡喃葡萄糖苷的生物合成。基于最近发现未受损的杨树叶片中积累了苯丙酮酸，推测糖苷的组成形成现在可能通过 Ehrlich 途径进行，该途径从苯丙氨酸转化为苯丙酮酸开始。
