title: A parthenogenesis gene of apomict origin elicits embryo formation from unfertilized eggs in a sexual plant.
abstract: Apomixis is a naturally occurring mode of asexual reproduction in flowering plants that results in seed formation without the involvement of meiosis or fertilization of the egg. Seeds formed on an apomictic plant contain offspring genetically identical to the maternal plant. Apomixis has significant potential for preserving hybrid vigor from one generation to the next in highly productive crop plant genotypes. Apomictic Pennisetum/Cenchrus species, members of the Poaceae (grass) family, reproduce by apospory. Apospory is characterized by apomeiosis, the formation of unreduced embryo sacs derived from nucellar cells of the ovary and, by parthenogenesis, the development of the unreduced egg into an embryo without fertilization. In Pennisetum squamulatum (L.) R.Br., apospory segregates as a single dominant locus, the apospory-specific genomic region (ASGR). In this study, we demonstrate that the PsASGR-BABY BOOM-like (PsASGR-BBML) gene is expressed in egg cells before fertilization and can induce parthenogenesis and the production of haploid offspring in transgenic sexual pearl millet. A reduction of PsASGR-BBML expression in apomictic F1 RNAi transgenic plants results in fewer visible parthenogenetic embryos and a reduction of embryo cell number compared with controls. Our results endorse a key role for PsASGR-BBML in parthenogenesis and a newly discovered role for a member of the BBM-like clade of APETALA 2 transcription factors. Induction of parthenogenesis by PsASGR-BBML will be valuable for installing parthenogenesis to synthesize apomixis in crops and will have further application for haploid induction to rapidly obtain homozygous lines for breeding.
authors: Department of Horticulture, University of Georgia Tifton Campus, Tifton, GA 31973.
authors: Joann A
authors: JA
authors: Conner
authors: Department of Horticulture, University of Georgia Tifton Campus, Tifton, GA 31973.
authors: Muruganantham
authors: M
authors: Mookkan
authors: Department of Horticulture, University of Georgia Tifton Campus, Tifton, GA 31973.
authors: Heqiang
authors: H
authors: Huo
authors: Department of Horticulture, University of Georgia Tifton Campus, Tifton, GA 31973.
authors: Keun
authors: K
authors: Chae
authors: Department of Horticulture, University of Georgia Tifton Campus, Tifton, GA 31973 pozias@uga.edu.
authors: Peggy
authors: P
authors: Ozias-Akins
mesh_terms: D000595:Amino Acid Sequence; D060832:Apomixis / Q000235:genetics*; D031741:Cenchrus / Q000196:embryology / Q000254:growth & development; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant / Q000235:genetics*; D008969:Molecular Sequence Data; D020411:Oligonucleotide Array Sequence Analysis; D056771:Ovule / Q000196:embryology / Q000235:genetics*; D010312:Parthenogenesis / Q000235:genetics*; D031782:Pennisetum / Q000196:embryology / Q000235:genetics; D010802:Phylogeny; D010940:Plant Proteins / Q000145:classification / Q000235:genetics; D030821:Plants, Genetically Modified; D006109:Poaceae / Q000196:embryology / Q000235:genetics*; D034622:RNA Interference; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012639:Seeds / Q000196:embryology / Q000235:genetics*; D017386:Sequence Homology, Amino Acid
chemical_list: D010940:Plant Proteins
keywords: AP2 transcription factor; BABY BOOM; Pennisetum; apomixis; parthenogenesis