Indole-3-acetic acid (IAA), a phytohormone auxin, may be involved in insect gall induction. We previously proposed that the IAA biosynthetic pathway is Trp → indole-3-acetaldoxime → indole-3-acetaldehyde (IAAld) → IAA or Trp → IAAld → IAA. In this study, we surveyed galling sawfly enzymes responsible for the rate-limiting steps using a heterologous protein expression system and identified PonAAS2, an aromatic aldehyde synthase, that catalyzed the conversion of Trp to IAAld. The PonAAS2 gene was highly expressed in early- and mid-stage larvae that contained high concentrations of IAA, but the expression level was almost negligible in larvae that had escaped from their gall in autumn and contained very low concentrations of IAA. An inhibitor of PonAAS2, obtained by screening a chemical library, inhibited IAA production in sawfly enzyme solution by 80%, suggesting the important role of this enzyme in IAA biosynthesis in sawfly.

吲哚-3-乙酸 (IAA) 是一种植物激素生长素，可能与虫瘿诱导有关。我们之前提出 IAA生物合成途径是 Trp → indole-3-acetaldoxime → indole-3-乙醛 (IAAld) → IAA 或 Trp → IAAld → IAA。在这项研究中，我们使用异源蛋白质表达系统调查了负责限速步骤的磨斑锯蝇酶，并鉴定了 PonAAS2，一种芳香醛合酶，可催化 Trp 转化为 IAAld。该PonAAS2基因在含有高浓度IAA的早期和中期幼虫中高度表达，但在秋季从它们的瘿中逃脱并且含有非常低浓度IAA的幼虫中表达水平几乎可以忽略不计。通过筛选化学文库获得的 PonAAS2 抑制剂将锯蝇酶溶液中 IAA 的产生抑制了 80%，表明该酶在锯蝇 IAA 生物合成中的重要作用。