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Review
. 2008 Jul;20(7):1738-46.
doi: 10.1105/tpc.108.060418. Epub 2008 Jul 22.

The evolving complexity of the auxin pathway

Steffen Lau  1 , Gerd Jürgens, Ive De Smet
Affiliations
Review

The evolving complexity of the auxin pathway

Steffen Lau et al. Plant Cell. 2008 Jul.
No abstract available

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Figures

Figure 1.
Figure 1.
Basics and Evolution of Auxin Signaling and Response. (A) Schematic representation of important domains and motifs of ARFs and AUX/IAAs. LxLxL resembles the repressive motif in ETHYLENE RESPONSE FACTOR–associated amphiphilic repression domains. DBD, B3 DNA binding domain; AD, activation domain; RD, repression domain. (B) Simplified scheme of auxin-responsive gene regulation through an activating ARF in the absence or presence of auxin. ASK1, ARABIDOPSIS SKP1-LIKE; CUL1, CULLIN1; E2, a conjugating enzyme; RBX1, RING-BOX PROTEIN1; RUB1, RELATED TO UBIQUITIN1. (C) Identical phenotypes of gain-of-function AUX/IAA (iaa12/bdl) and loss-of-function ARF (arf5/mp) auxin response mutants. (D) Phylogenetic scheme highlighting the evolution of auxin signaling and response, based on physiological and genomic data. The colored bars above the branches point out positive evidence for the indicated feature. It should be noted that only from mosses onward the available genome sequence has been analyzed in depth, and likewise the observed auxin responses display biological significance. Years taken from Yoon et al. (2004). *, fully sequenced genome; (), unconfirmed finding; NPA, naphthylphthalamic acid (an auxin transport inhibitor).
Figure 2.
Figure 2.
Upstream Regulation and Downstream Events of Auxin Signaling and Response. (A) Transcriptional regulation of AUX/IAAs. PAX1 regulation happens via a direct mechanism or through a feedback loop involving AXR3/IAA17. Dotted arrows indicate an unclear regulatory mechanism. (B) Regulation of the levels of ARF transcripts and proteins. Dotted arrow indicates an unclear regulatory mechanism. (C) Scheme of putative interactions between AUX/IAAs (IAA12/BDL), ARFs (ARF5/MP), a corepressor (TPL), a coactivator (MYB77), and proteins involved in histone acetylation (HAG1) and deacetylation (HDA19) in the presence and absence of auxin. Orange/yellow balloons indicate acetyl residues. (D) Model for hypophysis specification during embryogenesis, highlighting the role of IAA12/BDL and ARF5/MP in the embryo proper and an additional auxin response in combination with an MP-dependent putative mobile signal in the hypophysis. Hatched lines indicate MP-mediated auxin responses; red disc with a question mark indicates putative mobile signal. (E) Model for the asymmetric cell division of pericycle cells during lateral root initiation, focusing on SLR/IAA14, ARF7, ARF19, and their downstream targets LBD16 and LBD29.
Figure 3.
Figure 3.
Proposed Pathways of IAA Biosynthesis in Arabidopsis. The simplified scheme depicts the putative main pathways (black), some additional branches (gray), important precursors and intermediates, and the enzymes that are discussed in the text (gray boxes). The IAM pathway is most likely bacteria specific (dotted lines), and from IAOx via IG to IAN there are several intermediates that are not mentioned (hatched lines). CYP, cytochrome P450; IG, indole-3-methylglucosinolate; IAN, indole-3-acetonitrile; IAAld, indole-3-acetaldehyde.
See this image and copyright information in PMC

References

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