The main oxidative inactivation pathway of the plant hormone auxin

背景回顾：Inactivation of the phytohormone auxin plays important roles in plant development, and several enzymes have been implicated in auxin inactivation. 

主要发现：In this study, we show that the predominant natural auxin, indole-3-acetic acid (IAA), is mainly inactivated via the GH3-ILR1-DAO pathway. 

步骤1-IAA到IAA-氨基酸：IAA is first converted to IAA-amino acid conjugates by GH3 IAA-amidosynthetases. 

步骤2-IAA-氨基酸被水解，回到IAA：The IAA-amino acid conjugates IAA-aspartate (IAA-Asp) and IAA-glutamate (IAA-Glu) are storage forms of IAA and can be converted back to IAA by ILR1/ILL amidohydrolases. 

步骤3-IAA-氨基酸被氧化，再被水解后失活：We further show that DAO1 dioxygenase irreversibly oxidizes IAA-Asp and IAA-Glu into 2-oxindole-3-acetic acid-aspartate (oxIAA-Asp) and oxIAA-Glu, which are subsequently hydrolyzed by ILR1 to release inactive oxIAA. 

结论：This work established a complete pathway for the oxidative inactivation of auxin and defines the roles played by auxin homeostasis in plant development.

 摘 要 

植物激素生长素的失活在植物发育过程中发挥重要功能，目前已有一些酶被发现在生长素失活过程中起作用。本文中，作者发现自然界中主要的生长素吲哚-3-乙酸IAA通过GH3-ILR1-DAO途径被失活。IAA首先被GH3 IAA-氨基合酶转化成IAA-氨基酸结合物。IAA-氨基酸结合物IAA-天冬氨酸（IAA-Asp）和IAA-谷氨酸（IAA-Glu）是IAA的储存形式，能够被ILR1/ILL氨基水解酶重新转化为IAA。作者进一步发现DAO1双加氧酶能够不可逆地氧化IAA-Asp和IAA-Glu，形成2-羟基吲哚-3-乙酸-天冬氨酸（oxIAA-Asp）和2-羟基吲哚-3-乙酸-谷氨酸（oxIAA-Glu），后者会进一步被ILR1水解，释放出非活性的oxIAA。本文的研究结果建立了生长素IAA氧化失活的完整通路，揭示了生长素内稳态在植物发育过程中的重要作用。