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).