Distinct subclades of Aux/IAA genes are direct targets of ARF5/MP transcriptional regulation

Abstract

SummaryThe regulatory interactions between AUXIN RESPONSE FACTORS (ARFs) and Aux/IAA repressors play a central role in auxin signal transduction. Yet, the systems properties of this regulatory network are not well established.We generated a steroid-inducible ARF5/MONOPTEROS (MP) transgenic background to survey the involvement of this factor in the transcriptional regulation of the entire Aux/IAA family in Arabidopsis thaliana. Target genes of ARF5/MP identified by this approach were confirmed by chromatin immunoprecipitation, in vitro gel retardation assays and gene expression analyses.Our study shows that ARF5/MP is indispensable for the correct regulation of nearly one-half of all Aux/IAA genes, and that these targets coincide with distinct subclades. Further, genetic analyses demonstrate that the protein products of multiple Aux/IAA targets negatively feed back onto ARF5/MP activity.This work indicates that ARF5/MP broadly influences the expression of the Aux/IAA gene family, and suggests that such regulation involves the activation of specific subsets of redundantly functioning factors. These groups of factors may then act together to control various processes within the plant through negative feedback on ARF5. Similar detailed analyses of other Aux/IAA-ARF regulatory modules will be required to fully understand how auxin signal transduction influences virtually every aspect of plant growth and development.

PHABULOSA Mediates an Auxin Signaling Loop to Regulate Vascular Patterning in Arabidopsis

“…Potentially, the role for PHB and additional HD-ZIP III TFs is to facilitate auxin activation through MP (Lau et al, 2011;Krogan et al, 2014). We note that binding of PHB to the IAA20 promoter appears close to the auxin response element at 2200 bp, which previously was shown to attract MP (Krogan et al, 2014), and close to several auxin response elements within the 2500-bp region of the MP promoter (Lau et al, 2011).…”

“…F, A model summarizing our results in light of known interactions. Previously, it was shown that MP directly regulates its own expression (Lau et al 2011) as well as the expression of IAA20 (Krogan et al 2014), that IAA20 and IAA30, which are stable in the presence of auxin (Dreher et al 2006), can interact with MP (Vernoux et al 2011), and, therefore, that IAA20 and IAA30 likely repress MP function in their overlapping activity domains. Here, we show that HD-ZIP III TFs are needed for normal expression of IAA20/IAA30 and MP, and we hypothesize that PHB and MP cooperatively may activate IAA20 and IAA30.…”

“…PHB May Act to Stabilize the Auxin Response within the Xylem Axis through Both IAA20/IAA30 and MP As for most AUX/IAAs, auxin is known to rapidly induce the expression of IAA20 and IAA30 (Sato and Yamamoto, 2008a), and it was recently shown that MP is directly responsible for their activation (Krogan et al, 2014). The phenotypic effects generated by the overexpression of IAA20 and IAA30 are likely caused in part by sequestering of MP, as the introduction of a version of MP unable to interact with AUX/IAAs can partially suppress the strong phenotypes of a 35S::IAA20 line (Krogan et al, 2014).…”

“…The phenotypic effects generated by the overexpression of IAA20 and IAA30 are likely caused in part by sequestering of MP, as the introduction of a version of MP unable to interact with AUX/IAAs can partially suppress the strong phenotypes of a 35S::IAA20 line (Krogan et al, 2014). Hence, if IAA20 and IAA30 are dependent on MP for expression, while they also directly suppress the activity of MP, this generates a feedback system keeping these stable repressors to a certain level in the cell.…”

Auxin response cell-autonomously controls ground tissue initiation in the early Arabidopsis embryo

“…We aimed to identify novel MP target genes involved in the earliest events of embryonic root meristem initiation in the globular-stage embryo. As most MP target genes are expected to be activated by MP (17,(26)(27)(28)(29), we focused our analysis on the 145 down-regulated genes in the globular-stage embryo (SI Appendix, Table S1). Among these genes, ∼25% are transcription factors (36 of 145 genes) and 27 were also downregulated in heart-stage embryos (Fig.…”