A Molecular Framework for the Control of Adventitious Rooting by the TIR1/AFB2-Aux/IAA-Dependent Auxin Signaling in Arabidopsis

First author: Abdellah Lakehal; Affiliations: Umeå University (于默奥大学): Umeå, Sweden

Corresponding author: Catherine Bellini

In Arabidopsis thaliana, canonical auxin-dependent gene regulation is mediated by 23 transcription factors from the AUXIN RESPONSE FACTOR (ARF) family interacting with 29 auxin/indole acetic acid repressors (Aux/IAA), themselves forming coreceptor complexes with one of six TRANSPORT INHIBITOR1/AUXIN-SIGNALLING F-BOX (TIR1/AFB) PROTEINS. Different combinations of co-receptors drive specific sensing outputs, allowing auxin to control a myriad of processes. Considerable efforts have been made to discern the specificity of auxin action. However, owing to a lack of obvious phenotype in single loss-of-function mutants in Aux/IAA genes, most genetic studies have relied on gain-of-function mutants, which are highly pleiotropic. ARF6 and ARF8 are positive regulators of adventitious root initiation upstream of jasmonate, but the exact auxin co-receptor complexes controlling the transcriptional activity of these proteins was still unknown. Here using loss-of-function mutants we show that IAA6, IAA9 and IAA17 genes act additively in the control of AR initiation, and by performing protein-protein interaction analysis, we show that the corresponding proteins interact with ARF6 and/or ARF8 and likely repress their activity. We also demonstrate that TIR1 and AFB2 are positive regulators of adventitious root formation and suggest a dual role for TIR1 in the control of JA biosynthesis and conjugation, as revealed by upregulation of several JA biosynthesis genes in the tir1-1 mutant. We propose that in the presence of auxin, TIR1 and AFB2 form specific sensing complexes with IAA6, IAA9 and/or IAA17 that modulate JA homeostasis to control AR initiation.

在拟南芥中，经典的生长素依赖性基因调控是由来自生长素响应因子ARF家族的23个转录因子与29个生长素/吲哚乙酸抑制子Aux/IAA互作介导的，他们会与六个TIR1/AFB蛋白中的一个形成共受体复合物。不同的共受体组合会驱动特异的信号输出，从而使得生长素能够调控大量的生物学进程。已经有大量的研究工作着力于解析生长素作用特异性。然而，由于Aux/IAA基因单突变体缺乏明显的表型，大多数的遗传研究依赖于功能获得性突变体，但是这种功能获得具有高度的多效性。ARF6和ARF8基因在茉莉酸的上游发挥作用，正调控不定根的起始，但是具体哪个生长素共受体复合物作用于这些蛋白的转录活性还不清楚。本文中，作者通过利用功能丢失突变体发现IAA6、IAA9和IAA17基因对于控制不定根的起始具有加性效应；通过进一步的蛋白-蛋白互作分析，作者发现与ARF6和/或ARF8互作的蛋白很有可能还会抑制他们的活性。作者的研究还显示TIR1和AFB2基因是不定根形成的正向调控因子，说明了TIR1同时调控了茉莉酸的生物合成及共轭结合，tir1-1突变体中一些茉莉酸生物合成的基因受到了上调也可以证明这一推论。作者认为在存在生长素的情况下，TIR1和AFB2会与IAA6、IAA9和/或IAA17形成特异性感知复合体，通过介导植物体内茉莉酸的稳态控制不定根的起始。

通讯：Catherine Bellini (https://www.upsc.se/researchers/4621-control-of-adventitious-root-initiation-and-phloem-function-catherine-bellini.html#cv-dr-catherine-bellini)

个人简介：1984年，法国国立高等农业食品工程学校，学士；1985年，法国国立高等农业食品工程学校，硕士；1986年，法国巴黎第十一大学，硕士；1989年，法国巴黎第十一大学，博士；1989-1991年，意大利帕维亚大学，博士后。

研究方向：1. 拟南芥不定根起始的分子调控机制；2. 在韧皮部中表达的基因的功能鉴定。

doi: https://doi.org/10.1016/j.molp.2019.09.001

Journal: Molecular Plant

Published online: September 11, 2019