title: Challenging the paradigms of leaf evolution: Class III HD-Zips in ferns and lycophytes.
abstract: Despite the extraordinary significance leaves have for life on Earth, their origin and development remain vigorously debated. More than a century of paleobotanical, morphological, and phylogenetic research has still not resolved fundamental questions about leaves. Developmental genetic data are sparse in ferns, and comparative studies of lycophytes and seed plants have reached opposing conclusions on the conservation of a leaf developmental program. We performed phylogenetic and expression analyses of a leaf developmental regulator (Class III HD-Zip genes; C3HDZs) spanning lycophytes and ferns. We show that a duplication and neofunctionalization of C3HDZs probably occurred in the ancestor of euphyllophytes, and that there is a common leaf developmental mechanism conserved between ferns and seed plants. We show C3HDZ expression in lycophyte and fern sporangia and show that C3HDZs have conserved expression patterns during initiation of lateral primordia (leaves or sporangia). This expression is maintained throughout sporangium development in lycophytes and ferns and indicates an ancestral role of C3HDZs in sporangium development. We hypothesize that there is a deep homology of all leaves and that a sporangium-specific developmental program was coopted independently for the development of lycophyte and euphyllophyte leaves. This provides molecular genetic support for a paradigm shift in theories of lycophyte leaf evolution.
authors.affiliation: The New York Botanical Garden, 2900 Southern Blvd, Bronx, NY, 10458-5126, USA.|Instituto de Biología, Universidad Nacional Autónoma de México (UNAM), Mexico DF, 04510, Mexico.
authors.forename: Alejandra
authors.initials: A
authors.lastname: Vasco
authors.affiliation: The New York Botanical Garden, 2900 Southern Blvd, Bronx, NY, 10458-5126, USA.
authors.forename: Tynisha L
authors.initials: TL
authors.lastname: Smalls
authors.affiliation: Department of Botany, University of British Columbia, 6270 University Boulevard, Vancouver, BC, V6T 1Z4, Canada.|UBC Botanical Garden & Centre for Plant Research, University of British Columbia, 6804 Marine Drive SW, Vancouver, BC, V6T 1Z4, Canada.
authors.forename: Sean W
authors.initials: SW
authors.lastname: Graham
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, London, E1 4NS, UK.
authors.forename: Endymion D
authors.initials: ED
authors.lastname: Cooper
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, AB, T6G 2E9, Canada.|Department of Medicine, University of Alberta, Edmonton, AB, T6G 2E1, Canada.|BGI-Shenzhen, Beishan Industrial Zone, Yantian District, Shenzhen, 518083, China.
authors.forename: Gane Ka-Shu
authors.initials: GK
authors.lastname: Wong
authors.affiliation: The New York Botanical Garden, 2900 Southern Blvd, Bronx, NY, 10458-5126, USA.
authors.forename: Dennis W
authors.initials: DW
authors.lastname: Stevenson
authors.affiliation: The New York Botanical Garden, 2900 Southern Blvd, Bronx, NY, 10458-5126, USA.
authors.forename: Robbin C
authors.initials: RC
authors.lastname: Moran
authors.affiliation: The New York Botanical Garden, 2900 Southern Blvd, Bronx, NY, 10458-5126, USA. bambrose@nybg.org.
authors.forename: Barbara A
authors.initials: BA
authors.lastname: Ambrose
mesh_terms: D005075:Biological Evolution; D017124:Conserved Sequence; D029624:Ferns / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D018398:Homeodomain Proteins / Q000378:metabolism*; D008954:Models, Biological; D005810:Multigene Family; D010802:Phylogeny; D018515:Plant Leaves / Q000166:cytology / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism*
chemical_list: D018398:Homeodomain Proteins; D010940:Plant Proteins
keywords: Class III HD-Zip; enation theory; leaf evolution and development; megaphyll; microphyll; sterilization theory; telome theory