title: A single homeobox gene triggers phase transition, embryogenesis and asexual reproduction.
abstract: Plants characteristically alternate between haploid gametophytic and diploid sporophytic stages. Meiosis and fertilization respectively initiate these two different ontogenies(1). Genes triggering ectopic embryo development on vegetative sporophytic tissues are well described(2,3); however, a genetic control of embryo development from gametophytic tissues remains elusive. Here, in the moss Physcomitrella patens we show that ectopic overexpression of the homeobox gene BELL1 induces embryo formation and subsequently reproductive diploid sporophytes from specific gametophytic cells without fertilization. In line with this, BELL1 loss-of-function mutants have a wild-type phenotype, except that their egg cells are bigger and unable to form embryos. Our results identify BELL1 as a master regulator for the gametophyte-to-sporophyte transition in P. patens and provide mechanistic insights into the evolution of embryos that can generate multicellular diploid sporophytes. This developmental innovation facilitated the colonization of land by plants about 500 million years ago(4) and thus shaped our current ecosystems.
authors.affiliation: Plant Biotechnology, Faculty of Biology, University of Freiburg, Schaenzlestr. 1, 79104 Freiburg, Germany.
authors.forename: Nelly A
authors.initials: NA
authors.lastname: Horst
authors.affiliation: Department of Molecular Biology and Ecology of Plants, Tel-Aviv University, Tel-Aviv 69978, Israel.
authors.forename: Aviva
authors.initials: A
authors.lastname: Katz
authors.affiliation: Department of Molecular Biology and Ecology of Plants, Tel-Aviv University, Tel-Aviv 69978, Israel.
authors.forename: Idan
authors.initials: I
authors.lastname: Pereman
authors.affiliation: Plant Biotechnology, Faculty of Biology, University of Freiburg, Schaenzlestr. 1, 79104 Freiburg, Germany.
authors.forename: Eva L
authors.initials: EL
authors.lastname: Decker
authors.affiliation: Department of Molecular Biology and Ecology of Plants, Tel-Aviv University, Tel-Aviv 69978, Israel.|The Manna Center Program for Food Safety &Security, Tel Aviv University, Tel-Aviv 69978, Israel.
authors.forename: Nir
authors.initials: N
authors.lastname: Ohad
authors.affiliation: Plant Biotechnology, Faculty of Biology, University of Freiburg, Schaenzlestr. 1, 79104 Freiburg, Germany.|BIOSS - Centre for Biological Signalling Studies, 79104 Freiburg, Germany.|FRIAS - Freiburg Institute for Advanced Studies, 79104 Freiburg, Germany.
authors.forename: Ralf
authors.identifier: 0000-0002-5496-6711
authors.initials: R
authors.lastname: Reski
mesh_terms: D019068:Bryopsida / Q000196:embryology / Q000235:genetics* / Q000502:physiology; D004171:Diploidy; D005801:Genes, Homeobox / Q000235:genetics*; D055993:Germ Cells, Plant / Q000502:physiology; D006238:Haploidy; D012100:Reproduction, Asexual