title: Evolution of the ARF gene family in land plants: old domains, new tricks.
abstract: Auxin response factors (ARF) are key players in plant development. They mediate the cellular response to the plant hormone auxin by activating or repressing the expression of downstream developmental genes. The pivotal activation function of ARF proteins is enabled by their four-domain architecture, which includes both DNA-binding and protein dimerization motifs. To determine the evolutionary origin of this characteristic architecture, we built a comprehensive data set of 224 ARF-related protein sequences that represents all major living divisions of land plants, except hornworts. We found that ARFs are split into three subfamilies that could be traced back to the origin of the land plants. We also show that repeated events of extensive gene duplication contributed to the expansion of those three original subfamilies. Further examination of our data set uncovered a broad diversity in the structure of ARF transcripts and allowed us to identify an additional conserved motif in ARF proteins. We found that additional structural diversity in ARF proteins is mainly generated by two mechanisms: genomic truncation and alternative splicing. We propose that the loss of domains from the canonical, four-domain ARF structure has promoted functional shifts within the ARF family by disrupting either dimerization or DNA-binding capabilities. For instance, the loss of dimerization domains in some ARFs from moss and spikemoss genomes leads to proteins that are reminiscent of Aux/IAA proteins, possibly providing a clue on the evolution of these modulators of ARF function. We also assessed the functional impact of alternative splicing in the case of ARF4, for which we have identified a novel isoform in Arabidopsis thaliana. Genetic analysis showed that these two transcripts exhibit markedly different developmental roles in A. thaliana. Gene duplications, domain rearrangement, and post-transcriptional regulation have thus enabled a subtle control of auxin signaling through ARF proteins that may have contributed to the critical importance of these regulators in plant development and evolution.
authors.affiliation: Université de Lyon, Laboratoire de Reproduction et Développement des Plantes, UMR 5667, CNRS, INRA, Université Claude Bernard Lyon I, Ecole Normale Supérieure de Lyon, Lyon, France. cedric.finet@ens-lyon.org
authors.forename: Cédric
authors.initials: C
authors.lastname: Finet
authors.forename: Annick
authors.initials: A
authors.lastname: Berne-Dedieu
authors.forename: Charles P
authors.initials: CP
authors.lastname: Scutt
authors.forename: Ferdinand
authors.initials: F
authors.lastname: Marlétaz
mesh_terms: D020727:ADP-Ribosylation Factors / Q000235:genetics / Q000378:metabolism; D017398:Alternative Splicing; D017360:Arabidopsis / Q000235:genetics*; D044002:Bryophyta / Q000235:genetics; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D019143:Evolution, Molecular; D020440:Gene Duplication; D018506:Gene Expression Regulation, Plant; D015321:Gene Rearrangement; D017343:Genes, Plant; D007210:Indoleacetic Acids / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D005810:Multigene Family; D016366:Open Reading Frames; D010802:Phylogeny; D010937:Plant Growth Regulators / Q000378:metabolism*; D030821:Plants, Genetically Modified; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; D007210:Indoleacetic Acids; D008565:Membrane Proteins; D010937:Plant Growth Regulators; D014157:Transcription Factors; C097313:ADP-ribosylation factor related proteins; D020727:ADP-Ribosylation Factors