Molecular framework for TIR1/AFB-Aux/IAA-dependent auxin sensing controlling adventitious rooting in Arabidopsis

Abstract

In Arabidopsis thaliana, canonical auxin-dependent gene regulation is mediated by 23 transcription factors from the AUXIN RESPONSE FACTOR (ARF) family, most of which interact with 29 auxin/indole acetic acid (Aux/IAA) repressors, themselves forming, in the presence of auxin, coreceptor complexes with one of six TRANSPORT INHIBITOR1/AUXIN-SIGNALLING F-BOX PROTEINS (TIR1/AFB). 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 temporal and spatial 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. In this article, we describe a molecular framework for the role of several members of the auxin sensing machinery.Using loss-of-function mutants, we demonstrate that TIR1 and AFB2 are positive regulators, whereas IAA6, IAA9 and IAA17 are negative regulators of adventitious root (AR) formation. The three Aux/IAA proteins interact with ARF6 and/or ARF8, which we have previously shown to be positive regulators of AR formation upstream of jasmonate, and likely repress their activity. Our data also 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. In conclusion, 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.

Role of auxin homeostasis and response in nitrogen limitation and dark stimulation of adventitious root formation in petunia cuttings

“…Recent analysis of Arabidopsis gain-of-function mutants of specific Aux/IAA genes and a double loss-of-function mutant of ARF7 and ARF19 revealed that AR formation in leaf explants is inhibited when the functions of ARF7 and ARF19 are both impaired while the results further indicated that IAA18, IAA14 and IAA28 proteins are required to mediate auxin signalling during vascular proliferation, AR initiation and during both processes, respectively (Bustillo-Avendaño et al , 2018). In another recent study of AR formation in hypocotyls of intact Arabidopsis seedlings, analysis of knock-out mutants of IAA6 , IAA9 and IAA17 highlighted that the encoded proteins function as auxin repressors via down-regulation of ARF6 and/or ARF8, which act as positive regulators of etiolation-induced AR formation (Lakehal et al , 2019).…”

Integrated transgene and transcriptome reveal the molecular basis of MdWRKY87 positively regulate adventitious rooting in apple rootstock

“…It is well known auxin and cytokinin appear to play antagonistic roles in the adventitious rooting process. Among these TF and TR genes family, previous study has demonstrated that AUX/IAAs, AINTEGUMENTA (ANT), AINTEGUMENTA LIKE1 (AIL), WUSCHEL-RELATED HOMEOBOX (WOX), and type-B cytokinin Response Regulator (RR) family genes involved in adventitious rooting process (Ramıŕez-Carvajal et al, 2009;Rigal et al, 2012;Lakehal et al, 2019;Geng et al, 2023). In genes upregulated by MdWRKY87, WUSCHEL-RELATED HOMEOBOX11 (WOX11), and AINTEGUMENTA LIKE1 (AIL) are positive regulators of adventitious root formation.…”

“…It was well known that auxin play a dominant role in regulation of adventitious root formation (Lakehal et al, 2019). To further identify how MdWRKY87 regulate adventitious root formation, we analyzed the interaction between MdWRKY87 and auxin.…”

“…Among these DEGs, we found MdWRKY87 overexpression can activate the expression of adventitious rooting-induced genes, such as WOX11 and AIL, and the counterparts of WOX11 and AIL promote adventitious root formation in A.thaliana and poplar (Rigal et al, 2012;Hu and Xu, 2016;Geng et al, 2023). In addition, MdWRKY87 overexpression can inhibit the transcription of adventitious rootingrepressed genes, such as AUX/IAAs and RRs, and the counterparts of AUX/IAAs and type-B RRs inhibit adventitious root formation in Arabidopsis, apple, and poplar (Ramıŕez-Carvajal et al, 2009;Lakehal et al, 2019;Zhao et al, 2020). Similarly, it was demonstrated that PuWRKY75 interacted with PuMYB40 and directly co-regulate PuLRP1 and PuERF003 to promote adventitious root formation in P. ussuriensis (Wang et al, 2022).…”