title: RSL Class I Genes Controlled the Development of Epidermal Structures in the Common Ancestor of Land Plants.
abstract: The colonization of the land by plants, sometime before 470 million years ago, was accompanied by the evolution tissue systems [1-3]. Specialized structures with diverse functions-from nutrient acquisition to reproduction-derived from single cells in the outermost layer (epidermis) were important sources of morphological innovation at this time [2, 4, 5]. In extant plants, these structures may be unicellular extensions, such as root hairs or rhizoids [6-9], or multicellular structures, such as asexual propagules or secretory hairs (papillae) [10-12]. Here, we show that a ROOTHAIR DEFECTIVE SIX-LIKE (RSL) class I basic helix-loop-helix transcription factor positively regulates the development of the unicellular and multicellular structures that develop from individual cells that expand out of the epidermal plane of the liverwort Marchantia polymorpha; mutants that lack MpRSL1 function do not develop rhizoids, slime papillae, mucilage papillae, or gemmae. Furthermore, we discovered that RSL class I genes are also required for the development of multicellular axillary hairs on the gametophyte of the moss Physcomitrella patens. Because class I RSL proteins also control the development of rhizoids in mosses and root hairs in angiosperms [13, 14], these data demonstrate that the function of RSL class I genes was to control the development of structures derived from single epidermal cells in the common ancestor of the land plants. Class I RSL genes therefore controlled the generation of adaptive morphological diversity as plants colonized the land from the water.
authors.affiliation: Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, UK.
authors.forename: Hélène
authors.initials: H
authors.lastname: Proust
authors.affiliation: Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, UK.
authors.forename: Suvi
authors.initials: S
authors.lastname: Honkanen
authors.affiliation: Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, UK.
authors.forename: Victor A S
authors.initials: VA
authors.lastname: Jones
authors.affiliation: Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, UK.
authors.forename: Giulia
authors.initials: G
authors.lastname: Morieri
authors.affiliation: Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, UK.
authors.forename: Helen
authors.initials: H
authors.lastname: Prescott
authors.affiliation: Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, UK.
authors.forename: Steve
authors.initials: S
authors.lastname: Kelly
authors.affiliation: Graduate School of Science, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe 657-8501, Japan.
authors.forename: Kimitsune
authors.initials: K
authors.lastname: Ishizaki
authors.affiliation: Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Kohchi
authors.affiliation: Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, UK. Electronic address: liam.dolan@plants.ox.ac.uk.
authors.forename: Liam
authors.initials: L
authors.lastname: Dolan
mesh_terms: D000595:Amino Acid Sequence; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics* / Q000378:metabolism; D005075:Biological Evolution; D044002:Bryophyta / Q000235:genetics / Q000254:growth & development; D019068:Bryopsida / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D055993:Germ Cells, Plant / Q000254:growth & development; D007210:Indoleacetic Acids / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D010802:Phylogeny; D019441:Plant Epidermis / Q000166:cytology / Q000235:genetics* / Q000254:growth & development*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D007210:Indoleacetic Acids; D010940:Plant Proteins; D014157:Transcription Factors