title: Retrotransposon Proliferation Coincident with the Evolution of Dioecy in Asparagus.
abstract: Current phylogenetic sampling reveals that dioecy and an XY sex chromosome pair evolved once, or possibly twice, in the genus Asparagus Although there appear to be some lineage-specific polyploidization events, the base chromosome number of 2n = 2× = 20 is relatively conserved across the Asparagus genus. Regardless, dioecious species tend to have larger genomes than hermaphroditic species. Here, we test whether this genome size expansion in dioecious species is related to a polyploidization and subsequent chromosome fusion, or to retrotransposon proliferation in dioecious species. We first estimate genome sizes, or use published values, for four hermaphrodites and four dioecious species distributed across the phylogeny, and show that dioecious species typically have larger genomes than hermaphroditic species. Utilizing a phylogenomic approach, we find no evidence for ancient polyploidization contributing to increased genome sizes of sampled dioecious species. We do find support for an ancient whole genome duplication (WGD) event predating the diversification of the Asparagus genus. Repetitive DNA content of the four hermaphroditic and four dioecious species was characterized based on randomly sampled whole genome shotgun sequencing, and common elements were annotated. Across our broad phylogenetic sampling, Ty-1 Copia retroelements, in particular, have undergone a marked proliferation in dioecious species. In the absence of a detectable WGD event, retrotransposon proliferation is the most likely explanation for the precipitous increase in genome size in dioecious Asparagus species.
authors.affiliation: Department of Plant Biology, University of Georgia, Athens, Georgia 30602 Donald Danforth Plant Science Center, St. Louis, Missouri 63132 aharkess@danforthcenter.org.
authors.forename: Alex
authors.identifier: 0000-0002-2035-0871
authors.initials: A
authors.lastname: Harkess
authors.affiliation: Dipartimento di AGRARIA, Università Mediterranea di Reggio Calabria, Salita Melissari, 89124 Reggio Calabria, Italy Institute of Biosciences and BioResources, Division of Palermo, National Research Council, 900129 Palermo, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Mercati
authors.affiliation: Institute of Biosciences and BioResources, Division of Palermo, National Research Council, 900129 Palermo, Italy.
authors.forename: Loredana
authors.initials: L
authors.lastname: Abbate
authors.affiliation: Donald Danforth Plant Science Center, St. Louis, Missouri 63132.
authors.forename: Michael
authors.initials: M
authors.lastname: McKain
authors.affiliation: Division of Biological Sciences, University of Missouri, Columbia, Missouri 65211.
authors.forename: J Chris
authors.initials: JC
authors.lastname: Pires
authors.affiliation: Consiglio per la Ricerca in Agricoltura e l'analisi dell'economia agraria (CREA), Research Unit for Vegetable Crops, Montanaso Lombardo, 26836 Lodi, Italy.
authors.forename: Tea
authors.initials: T
authors.lastname: Sala
authors.affiliation: Dipartimento di AGRARIA, Università Mediterranea di Reggio Calabria, Salita Melissari, 89124 Reggio Calabria, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Sunseri
authors.affiliation: Consiglio per la Ricerca in Agricoltura e l'analisi dell'economia agraria (CREA), Research Unit for Vegetable Crops, Montanaso Lombardo, 26836 Lodi, Italy.
authors.forename: Agostino
authors.initials: A
authors.lastname: Falavigna
authors.affiliation: Department of Plant Biology, University of Georgia, Athens, Georgia 30602.
authors.forename: Jim
authors.initials: J
authors.lastname: Leebens-Mack
mesh_terms: D027761:Asparagus Plant / Q000235:genetics*; D019143:Evolution, Molecular; D059646:Genome Size; D018745:Genome, Plant; D057850:Hermaphroditic Organisms / Q000235:genetics; D010802:Phylogeny; D011123:Polyploidy; D018626:Retroelements / Q000235:genetics*; D012730:Sex Chromosomes / Q000235:genetics
chemical_list: D018626:Retroelements
keywords: Asparagus; dioecy; genome size; sex chromosomes; transposons