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Genes (Basel). 2018 May 29;9(6). pii: E277. doi: 10.3390/genes9060277.

Size and Content of the Sex-Determining Region of the Y Chromosome in Dioecious Mercurialis annua, a Plant with Homomorphic Sex Chromosomes.

Author information

1
Department of Ecology and Evolution, University of Lausanne, 1015 Lausanne, Switzerland. parisveltsos@gmail.com.
2
Department of Biology, Jordan Hall, 1001 East Third Street, Indiana University, Bloomington, IN 47405, USA. parisveltsos@gmail.com.
3
Department of Ecology and Evolution, University of Lausanne, 1015 Lausanne, Switzerland. guillaume.cossard@unil.ch.
4
Faculty of Biology and Medicine, University of Lausanne, Bâtiment Génopode, 1014 Lausanne, Switzerland. emmanuel.beaudoing@unil.ch.
5
National Centre for Genomic Resources (CNRGV), 24 Chemin de Borde Rouge-Auzeville-CS52627, 31326 Castanet Tolosan Cedex, France. genseric.beydon@toulouse.inra.fr.
6
Department of Ecology and Evolution, University of Lausanne, 1015 Lausanne, Switzerland. dessislava.savovabianchi@unil.ch.
7
Department of Ecology and Evolution, University of Lausanne, 1015 Lausanne, Switzerland. camille.roux.1983@gmail.com.
8
CNRS, University of Lille, UMR 8198-Evo-Eco-Paleo, F-59000 Lille, France. camille.roux.1983@gmail.com.
9
Department of Ecology and Evolution, University of Lausanne, 1015 Lausanne, Switzerland. santiago.gonzalez-martinez@pierroton.inra.fr.
10
BIOGECO, INRA, University of Bordeaux, 33610 Cestas, France. santiago.gonzalez-martinez@pierroton.inra.fr.
11
Department of Ecology and Evolution, University of Lausanne, 1015 Lausanne, Switzerland. John.Pannell@unil.ch.

Abstract

Dioecious plants vary in whether their sex chromosomes are heteromorphic or homomorphic, but even homomorphic sex chromosomes may show divergence between homologues in the non-recombining, sex-determining region (SDR). Very little is known about the SDR of these species, which might represent particularly early stages of sex-chromosome evolution. Here, we assess the size and content of the SDR of the diploid dioecious herb Mercurialis annua, a species with homomorphic sex chromosomes and mild Y-chromosome degeneration. We used RNA sequencing (RNAseq) to identify new Y-linked markers for M. annua. Twelve of 24 transcripts showing male-specific expression in a previous experiment could be amplified by polymerase chain reaction (PCR) only from males, and are thus likely to be Y-linked. Analysis of genome-capture data from multiple populations of M. annua pointed to an additional six male-limited (and thus Y-linked) sequences. We used these markers to identify and sequence 17 sex-linked bacterial artificial chromosomes (BACs), which form 11 groups of non-overlapping sequences, covering a total sequence length of about 1.5 Mb. Content analysis of this region suggests that it is enriched for repeats, has low gene density, and contains few candidate sex-determining genes. The BACs map to a subset of the sex-linked region of the genetic map, which we estimate to be at least 14.5 Mb. This is substantially larger than estimates for other dioecious plants with homomorphic sex chromosomes, both in absolute terms and relative to their genome sizes. Our data provide a rare, high-resolution view of the homomorphic Y chromosome of a dioecious plant.

KEYWORDS:

RNA sequencing (RNAseq); bacterial artificial chromosomes (BAC); gene density; genetic map; transposable element

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