Auxin signaling through SCFTIR1/AFBs mediates feedback regulation of IAA biosynthesis

Abstract

We previously reported that exogenous application of auxin to Arabidopsis seedlings resulted in downregulation of indole-3-acetic acid (IAA) biosynthesis genes in a feedback manner. In this study, we investigated the involvement of the SCF-mediated signaling pathway in feedback regulation of the indole-3-pyruvic acid-mediated auxin biosynthesis pathway in Arabidopsis. Application of PEO-IAA, an inhibitor of the IAA signal transduction pathway, to wild-type seedlings resulted in increased endogenous IAA levels in roots. Endogenous IAA levels in the auxin-signaling mutants axr2-1, axr3-3, and tir1-1afb1-1afb2-1afb3-1 also increased. Furthermore, YUCCA (YUC) gene expression was repressed in response to auxin treatment, and expression of YUC7 and YUC8 increased in response to PEO-IAA treatment. YUC genes were also induced in auxin-signaling mutants but repressed in TIR1-overexpression lines. These observations suggest that the endogenous IAA levels are regulated by auxin biosynthesis in a feedback manner, and the Aux/IAA and SCF-mediated auxin-signaling pathway regulates the expression of YUC genes.

Dual role of auxin in regulating plant defense and bacterial virulence gene expression duringPseudomonas syringae PtoDC3000 pathogenesis

“…2D), provides a reasonable explanation for this result, as we have previously shown that elevated levels of endogenous auxin promotes growth of PtoDC3000 (32). Further, our observation that tir1 afb1 afb4 afb5 plants exhibit elevated IAA levels is consistent with recent findings that homeostasis of endogenous IAA is maintained by feedback regulation through the canonical auxin signaling pathway (27). Consistent with the role for IAA in suppressing SA signaling, we demonstrated that the tir1 afb1 afb4 afb5 mutant plants exhibited significantly reduced expression of PR-1 and reduced SA levels compared to WT plants at 24h post inoculation ( Fig.…”

“…It is not immediately obvious why the tir1 afb1 afb4 afb5 mutant, which has decreased auxin-responsive gene expression, exhibits enhanced susceptibility to PtoDC3000. We hypothesized that the tir1 afb1 afb4 afb5 plants might accumulate elevated levels of IAA, due to disruption of the feedback mechanism that normally maintains IAA homeostasis in WT plants (27) and that this elevated IAA promotes susceptibility. To investigate whether the enhanced pathogen growth in tir1 afb1 afb4 afb5 plants is correlated with elevated IAA in host tissue, we quantified free IAA levels in WT Col-0 and tir1 afb1 afb4 afb5, in both PtoDC3000-infected and mock-treated plants at 24h post inoculation.…”

Origin and evolution of the nuclear auxin response system

“…We further selected several known auxin-responsive genes in angiosperms and determined the expression of their homologues in our RNA-seq dataset. It is known that class II homeodomain-leucine zipper ( C2HDZ ), WIP , and YUCCA ( YUC ) genes are regulated by auxin in A. thaliana (Crawford et al, 2015; Sawa et al, 2002; Takato et al, 2017). We identified C2HDZ and WIP to be commonly activated by auxin in all land plants in our RNA-seq (note that no WIP gene was identified in the A. agrestis assembly).…”

The Roles of Auxin Biosynthesis YUCCA Gene Family in Plants

“…For instance, only limited information is available for the molecular modifications of YUC genes or proteins to regulate active auxin levels. It was found that active auxin itself could regulate YUC gene expressions via a negative feedback manner in Arabidopsis [159,160]. Under excess auxin conditions, the four essential YUCs (YUC1, 2, 4, and 6) were transcriptionally downregulated and upregulated under auxin-deficient conditions [159].…”