Jenness Mark, Tayengwa Reuben, House Lillyanna, Cao Shiyun, Báez Román Ramos, Nath Seema, Pritchard Candace A, Sharma Anket, Mergner Julia, Rivière Frédèric, Meinnel Thierry, Giglione Carmela, Kuster Bernhard, Blakeslee Joshua J, Nemhauser Jennifer L, Zheng Ning, Murphy Angus S, Peer Wendy Ann
Department of Pant Science and Landscape Architecture, University of Maryland, College Park, MD 20742, USA.
Howard Hughes Medical Institute, Department of Pharmacology, University of Washington, Seattle, WA 98195, USA.
Plant Physiol. 2025 Aug 4;198(4). doi: 10.1093/plphys/kiaf330.
Catabolism of the auxin indole-3-acetic acid (IAA) to terminate cellular responses primarily occurs in three steps: (i) conjugation of IAA to Asp/Glu, (ii) oxidation of the indole ring by DIOXYGENASE FOR AUXIN OXIDATION (DAO), and (iii) amidohydrolase cleavage of Asp/Glu. This study examines if IAA oxidation historically associated with membranes is mediated by DAO isoforms and if the oxidized auxin product (oxIAA) retains nominal functionality. We show that Arabidopsis thaliana DAO1 exhibits both soluble and auxin-dependent plasma membrane association, and that oxIAA exhibits weak "anti-auxin" activity. Both soluble and membrane-associated DAO1 primarily oxidized IAAsp. DAO2 activity was enzymatically similar to DAO1 and occurred where IAA levels were high. DAO1 and DAO2 functioned synergistically in adventitious root formation and in temperature-dependent petal development. In vitro assays showed that oxIAA acts as a molecular glue between repressor auxin/indole-3-acetic acid (AUX/IAA) proteins IAA7 and IAA17 and Transport Inhibitor Response 1 (TIR1) auxin co-receptors but is readily outcompeted by IAA. Biolayer interferometry and yeast degradation assays indicated weak "anti-auxin" activity, as oxIAA enhances IAA7-TIR1 interactions while retarding IAA7 and IAA17 degradation. In a low auxin/quiescent interval that precedes auxin-triggered apical hook opening in etiolated seedlings, IAA7 gain-of-function and loss-of-function mutants exhibited early apical hook opening similar to dao1, and application of oxIAA to etiolated dao1 apical hooks partially rescued the phenotype. The weak "anti-auxin" activity of oxIAA during transitional growth is an important reminder of the evolutionary processes that forge adaptive plant growth responses.
生长素吲哚 - 3 - 乙酸（IAA）的分解代谢以终止细胞反应主要发生在三个步骤：（i）IAA与天冬氨酸/谷氨酸结合，（ii）由生长素氧化双加氧酶（DAO）氧化吲哚环，以及（iii）天冬氨酸/谷氨酸的酰胺水解酶裂解。本研究考察了历史上与膜相关的IAA氧化是否由DAO同工型介导，以及氧化的生长素产物（oxIAA）是否保留标称功能。我们表明，拟南芥DAO1既表现出可溶性又表现出依赖生长素的质膜结合，并且oxIAA表现出弱的“抗生长素”活性。可溶性和膜相关的DAO1主要氧化IAAsp。DAO2的活性在酶学上与DAO1相似，并且在IAA水平高的地方发生。DAO1和DAO2在不定根形成和温度依赖性花瓣发育中协同发挥作用。体外试验表明，oxIAA作为阻遏生长素/吲哚 - 3 - 乙酸（AUX/IAA）蛋白IAA7和IAA17与运输抑制剂响应1（TIR1）生长素共受体之间的分子胶水，但很容易被IAA竞争取代。生物层干涉术和酵母降解试验表明其具有弱的“抗生长素”活性，因为oxIAA增强了IAA7 - TIR1相互作用，同时延缓了IAA7和IAA17的降解。在黄化幼苗中生长素触发顶端弯钩打开之前的低生长素/静止间隔期，IAA7功能获得和功能缺失突变体表现出与dao1相似的早期顶端弯钩打开，并且将oxIAA应用于黄化的dao1顶端弯钩部分挽救了该表型。oxIAA在过渡生长期间的弱“抗生长素”活性是对形成适应性植物生长反应的进化过程的重要提醒。
