title: Unraveling the evolution of auxin signaling.
abstract: Auxin signaling is central to plant growth and development, yet hardly anything is known about its evolutionary origin. While the presence of key players in auxin signaling has been analyzed in various land plant species, similar analyses in the green algal lineages are lacking. Here, we survey the key players in auxin biology in the available genomes of Chlorophyta species. We found that the genetic potential for auxin biosynthesis and AUXIN1 (AUX1)/LIKE AUX1- and P-GLYCOPROTEIN/ATP-BINDING CASSETTE subfamily B-dependent transport is already present in several single-celled and colony-forming Chlorophyta species. In addition, our analysis of expressed sequence tag libraries from Coleochaete orbicularis and Spirogyra pratensis, green algae of the Streptophyta clade that are evolutionarily closer to the land plants than those of the Chlorophyta clade, revealed the presence of partial AUXIN RESPONSE FACTORs and/or AUXIN/INDOLE-3-ACETIC ACID proteins (the key factors in auxin signaling) and PIN-FORMED-like proteins (the best-characterized auxin-efflux carriers). While the identification of these possible AUXIN RESPONSE FACTOR- and AUXIN/INDOLE-3-ACETIC ACID precursors and putative PIN-FORMED orthologs calls for a deeper investigation of their evolution after sequencing more intermediate genomes, it emphasizes that the canonical auxin response machinery and auxin transport mechanisms were, at least in part, already present before plants "moved" to land habitats.
authors.affiliation: Department of Plant Systems Biology, Flanders Institute for Biotechnology, 9052 Ghent, Belgium. ivsme@psb.vib-ugent.be
authors.forename: Ive
authors.initials: I
authors.lastname: De Smet
authors.forename: Ute
authors.initials: U
authors.lastname: Voss
authors.forename: Steffen
authors.initials: S
authors.lastname: Lau
authors.forename: Michael
authors.initials: M
authors.lastname: Wilson
authors.forename: Ning
authors.initials: N
authors.lastname: Shao
authors.forename: Ruth E
authors.initials: RE
authors.lastname: Timme
authors.forename: Ranjan
authors.initials: R
authors.lastname: Swarup
authors.forename: Ian
authors.initials: I
authors.lastname: Kerr
authors.forename: Charlie
authors.initials: C
authors.lastname: Hodgman
authors.forename: Ralph
authors.initials: R
authors.lastname: Bock
authors.forename: Malcolm
authors.initials: M
authors.lastname: Bennett
authors.forename: Gerd
authors.initials: G
authors.lastname: Jürgens
authors.forename: Tom
authors.initials: T
authors.lastname: Beeckman
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics; D001692:Biological Transport; D002696:Chlamydomonas / Q000235:genetics; D000460:Chlorophyta / Q000235:genetics* / Q000378:metabolism; D019143:Evolution, Molecular; D007210:Indoleacetic Acids / Q000378:metabolism*; D008969:Molecular Sequence Data; D010802:Phylogeny; D011401:Promoter Regions, Genetic / Q000235:genetics; D011506:Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics*
chemical_list: D007210:Indoleacetic Acids; D011506:Proteins