title: Apomictic and sexual germline development differ with respect to cell cycle, transcriptional, hormonal and epigenetic regulation.
abstract: Seeds of flowering plants can be formed sexually or asexually through apomixis. Apomixis occurs in about 400 species and is of great interest for agriculture as it produces clonal offspring. It differs from sexual reproduction in three major aspects: (1) While the sexual megaspore mother cell (MMC) undergoes meiosis, the apomictic initial cell (AIC) omits or aborts meiosis (apomeiosis); (2) the unreduced egg cell of apomicts forms an embryo without fertilization (parthenogenesis); and (3) the formation of functional endosperm requires specific developmental adaptations. Currently, our knowledge about the gene regulatory programs underlying apomixis is scarce. We used the apomict Boechera gunnisoniana, a close relative of Arabidopsis thaliana, to investigate the transcriptional basis underlying apomeiosis and parthenogenesis. Here, we present the first comprehensive reference transcriptome for reproductive development in an apomict. To compare sexual and apomictic development at the cellular level, we used laser-assisted microdissection combined with microarray and RNA-Seq analyses. Conservation of enriched gene ontologies between the AIC and the MMC likely reflects functions of importance to germline initiation, illustrating the close developmental relationship of sexuality and apomixis. However, several regulatory pathways differ between sexual and apomictic germlines, including cell cycle control, hormonal pathways, epigenetic and transcriptional regulation. Enrichment of specific signal transduction pathways are a feature of the apomictic germline, as is spermidine metabolism, which is associated with somatic embryogenesis in various plants. Our study provides a comprehensive reference dataset for apomictic development and yields important new insights into the transcriptional basis underlying apomixis in relation to sexual reproduction.
authors.affiliation: Institute of Plant Biology & Zürich-Basel Plant Science Center, University of Zürich, Zürich, Switzerland.
authors.forename: Anja
authors.initials: A
authors.lastname: Schmidt
authors.affiliation: Institute of Plant Biology & Zürich-Basel Plant Science Center, University of Zürich, Zürich, Switzerland.
authors.forename: Marc W
authors.initials: MW
authors.lastname: Schmid
authors.affiliation: Institute of Clinical Molecular Biology, Christian-Albrechts University, Kiel, Germany.
authors.forename: Ulrich C
authors.initials: UC
authors.lastname: Klostermeier
authors.affiliation: Functional Genomics Center Zürich, UZH/ETH Zürich, Zürich, Switzerland.
authors.forename: Weihong
authors.initials: W
authors.lastname: Qi
authors.affiliation: Institute of Plant Biology & Zürich-Basel Plant Science Center, University of Zürich, Zürich, Switzerland.
authors.forename: Daniela
authors.initials: D
authors.lastname: Guthörl
authors.affiliation: Institute of Plant Biology & Zürich-Basel Plant Science Center, University of Zürich, Zürich, Switzerland.
authors.forename: Christian
authors.initials: C
authors.lastname: Sailer
authors.affiliation: Institute of Plant Biology & Zürich-Basel Plant Science Center, University of Zürich, Zürich, Switzerland.
authors.forename: Manuel
authors.initials: M
authors.lastname: Waller
authors.affiliation: Institute of Clinical Molecular Biology, Christian-Albrechts University, Kiel, Germany.
authors.forename: Philip
authors.initials: P
authors.lastname: Rosenstiel
authors.affiliation: Institute of Plant Biology & Zürich-Basel Plant Science Center, University of Zürich, Zürich, Switzerland.
authors.forename: Ueli
authors.initials: U
authors.lastname: Grossniklaus
mesh_terms: D060832:Apomixis / Q000235:genetics*; D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development; D002453:Cell Cycle / Q000235:genetics; D044127:Epigenesis, Genetic; D018506:Gene Expression Regulation, Plant; D005854:Germ Cells / Q000254:growth & development; D008540:Meiosis / Q000235:genetics; D012098:Reproduction / Q000235:genetics; D012639:Seeds / Q000235:genetics / Q000254:growth & development; D046468:Sexual Development / Q000235:genetics*; D014158:Transcription, Genetic