Indole-3-acetamide (IAM) is the first confirmed auxin biosynthetic intermediate in some plant pathogenic bacteria. Exogenously applied IAM or production of IAM by overexpressing the bacterial iaaM gene in Arabidopsis causes auxin overproduction phenotypes. However, it is still inconclusive whether plants use IAM as a key precursor for auxin biosynthesis. Herein, we reported the isolation IAM HYDROLASE 1 (IAMH1) gene in Arabidopsis from a forward genetic screen for IAM-insensitive mutants that display normal auxin sensitivities. IAMH1 has a close homolog named IAMH2 that is located right next to IAMH1 on chromosome IV in Arabidopsis. We generated iamh1 iamh2 double mutants using our CRISPR/Cas9 gene editing technology. We showed that disruption of the IAMH genes rendered Arabidopsis plants resistant to IAM treatments and also suppressed the iaaM overexpression phenotypes, suggesting that IAMH1 and IAMH2 are the main enzymes responsible for converting IAM into indole-3-acetic acid (IAA) in Arabidopsis. The iamh double mutants did not display obvious developmental defects, indicating that IAM does not play a major role in auxin biosynthesis under normal growth conditions. Our findings provide a solid foundation for clarifying the roles of IAM in auxin biosynthesis and plant development.

吲哚-3-乙酰胺（IAM）是某些植物病原细菌中首个被确认的生长素生物合成中间体。外源施用IAM或通过在拟南芥中过表达细菌iaaM基因来产生IAM会导致植物生长素的过量生产表型。然而，植物是否使用IAM作为生长素生物合成的关键前体仍是不确定的。在这里，我们报道了从拟南芥中分离的IAM HYDROLASE 1（IAMH1）基因，从显示正常生长素敏感性的IAM不敏感突变体的正向遗传筛选中获得。IAMH1有一个紧密的同系物IAMH2，紧邻IAMH1在拟南芥的IV染色体上。我们使用CRISPR / Cas9基因编辑技术生成了iamh1 iamh2双突变体。我们发现IAMH基因的破坏使拟南芥植物对IAM处理具有抗性，并且还抑制了iaaM过表达表型，这表明IAMH1和IAMH2是负责将IAM转化为拟南芥中吲哚-3-乙酸（IAA）的主要酶。该iamh双突变体没有显示出明显的发育缺陷，表明IAM在正常生长条件下在生长素生物合成中不发挥主要作用。我们的发现为阐明IAM在生长素生物合成和植物发育中的作用提供了坚实的基础。