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

摘要

In Arabidopsis thaliana,canonical auxin-dependent gene regulation is mediated by 23 transcription factors from the AUXIN RESPONSE FACTOR(ARF)family that interact with auxin/indole acetic acid repressors(Aux/IAAs),which themselves form co-receptor complexes with one of six TRANSPORT INHIBITOR1/AUXIN-SIGNALLlNG F-BOX(TIR1/AFB)proteins.Different combinations of co-receptors drive specific sensing outputs,allowing auxin to control a myriad of processes.ARF6 and ARF8 are positive regulators of adventitious root initiation upstream of jasmonate,but the exact auxin co-receptor complexes control-ling the transcriptional activity of these proteins has remained unknown.Here,using loss-of-function mu-tants we show that three Aux/IAA genes,IAA6,IAA9,and IAA 17,act additively in the control of adventitious root(AR)initiation.These three IAA proteins interact with ARF6 and/or ARF8 and likely repress their activity in AR development.We show that TIR1 and AFB2 are positive regulators of AR formation and TIR1 plays a dual role in the control of jasmonic acid(JA)biosynthesis and conjugation,as several JA biosynthesis genes are up-regulated in the tir1-1 mutant.These results lead us to propose that in the presence of auxin,TIR1 and AFB2 form specific sensing complexes with IAA6,IAA9,and/or IAA 17 to modulate JA homeostasis and control AR initiation.