Developmental specificity of auxin response by pairs of ARF and Aux/IAA transcriptional regulators

Abstract

The plant hormone auxin elicits many specific contextdependent developmental responses. Auxin promotes degradation of Aux/IAA proteins that prevent transcription factors of the auxin response factor (ARF) family from regulating auxin-responsive target genes. Aux/IAAs and ARFs are represented by large gene families in Arabidopsis. Here we show that stabilization of BDL/ IAA12 or its sister protein IAA13 prevents MP/ARF5-dependent embryonic root formation whereas stabilized SHY2/IAA3 interferes with seedling growth. Although both bdl and shy2-2 proteins inhibited MP/ARF5-dependent reporter gene activation, shy2-2 was much less efficient than bdl to interfere with embryonic root initiation when expressed from the BDL promoter. Similarly, MP was much more efficient than ARF16 in this process. When expressed from the SHY2 promoter, both shy2-2 and bdl inhibited cell elongation and auxin-induced gene expression in the seedling hypocotyl. By contrast, gravitropism and auxin-induced gene expression in the root, which were promoted by functionally redundant NPH4/ ARF7 and ARF19 proteins, were inhibited by shy2-2, but not by bdl protein. Our results suggest that auxin signals are converted into specific responses by matching pairs of coexpressed ARF and Aux/IAA proteins.

Embryogenesis: Pattern Formation from a Single Cell

“…The vascular systems in these mutants are severely reduced, the cotyledons fused, and hypocotyl and root replaced by a short undifferentiated basal peg (Berleth and Jurgens, 1993). Similar phenotypes are observed in mutations suppressing degradation of the closely related Aux/IAA proteins BODENLOS (BDL/IAA12) and IAA13 (Weijers et al, 2005b). MP and BDL proteins have been shown to interact in vivo (Hamann et al, 2002;Weijers et al, 2006) and it seems likely that both BDL and IAA13 inhibit MP activity.…”

MLN4924 Is an Efficient Inhibitor of NEDD8 Conjugation in Plants

“…Indeed, we observed an MLN4924-dependent accumulation of the AUX/IAA protein BODENLOS (BDL)/IAA12 by examining a transgenic line expressing a translational fusion between BDL and the reporter GUS (BDL:BDL:GUS; Fig. 3D; Weijers et al, 2005). We further observed that the transcripts of two representative auxin-induced genes, IAA3 and IAA13, whose expression is normally repressed by AUX/IAAs and induced following AUX/IAA degradation, is compromised in MLN4924-treated wild-type seedlings and even more so in the genetically sensitized axr1-12 mutants (Fig.…”

What Makes eachAux/IAAGene Unique in its Gene Family, Expression Pattern or Properties of the Gene Product?

“…In the latest issue of Plant Physiology we also reported our results on this question 5 by taking advantage of the msg2/iaa19 mutants, which exhibit fewer defects than the other dominant Aux/IAA mutants. 6,7 Figure 1 summarizes our results as well as those of Weijers et al 4 In our experiments, cDNA of msg2, axr2/iss7 8 or slr-1/iaa14 9 was driven by the MSG2 or AXR2 promoter. Weijers et al expressed the bdl/iaa12 10 or shy2/iaa3 11 cDNA by the BDL or SHY2 promoters.…”

“…In this case, each mAux/IAAs should induce qualitatively different defects even if expressed by the same promoter. This question has been addressed before by Knox et al 3 and Weijers et al 4 by the use of the promoter-swapping strategy. In the latest issue of Plant Physiology we also reported our results on this question 5 by taking advantage of the msg2/iaa19 mutants, which exhibit fewer defects than the other dominant Aux/IAA mutants.…”

“…This conclusion is essentially the same as that reached by the previous study. 4 The importance of gene expression has been widely recognized in studies of gene function. Thus, it would be surprising if each mAux/IAA protein had distinct characteristics, and the next question would be: What properties of the Aux/IAA proteins make them distinct from each other?…”