The evolution of sex chromosomes in the genus Rumex (Polygonaceae): Identification of a new species with heteromorphic sex chromosomes

Abstract

The structural features and evolutionary state of the sex chromosomes of the XX/XY species of Rumex are unknown. Here, we report a study of the meiotic behaviour of the XY bivalent in Rumex acetosella and R. suffruticosus, a new species which we describe cytogenetically for the first time in this paper, and also that of the XY(1)Y(2) trivalent of R. acetosa by both conventional cytogenetic techniques and analysis of synaptonemal complex formation. Fluorescent in situ hybridization with satellite DNA and rDNA sequences as probes was used to analyse the degree of cytogenetic differentiation between the X and Y chromosomes in order to depict their evolutionary stage in the three species. Contrasting with the advanced state of genetic differentiation between the X and the Y chromosomes in R. acetosa, we have found that R. acetosella and R. suffruticosus represent an early stage of genetic differentiation between sex chromosomes. Our findings further demonstrate the usefulness of the genus Rumex as a model for analysing the evolution of sex chromosomes in plants, since within this genus it is now possible to study the different levels of genetic differentiation between the sex chromosomes and to analyse their evolutionary history from their origin.

Evolution of Neo-Sex Chromosomes inSilene diclinis

“…For example, in the dioecious species in Rumex section Acetosa having two Y chromosomes and a single X these three chromosomes form a trivalent, Y1-X-Y2, and gametes containing either the X or Y1 and Y2. Consequently female plants are 2n ¼ 12 1 XX and males are 2n ¼ 12 1 XY1Y2 (Cunado et al 2007;Navajas-Perez et al 2009). In S. diclinis females and males have the same chromosome number with females being 2n ¼ 20 1 XXneo-Xneo-X and males 2n ¼ 20 1 Xneo-XY1Y2.…”

“…Trivalent formation comprising Y1 X Y2 has been observed both in H. japonicus (Shephard et al 2000) and in a number of dioecious species in the genus Rumex (Cunado et al 2007;Navajas-Perez et al 2009). Here we report that the plant species Silene diclinis has multiple sex chromosomes that form a chain of four during meiosis metaphase I.…”

The role of repetitive DNA in structure and evolution of sex chromosomes in plants

“…RAE180 is a major component of the Y1 chromosome, but is also located on the Y2 and at a single autosomal locus. RAYSI is restricted only to the Y chromosomes in R. acetosa and also occurs in several related species with multiple sex chromosome systems (Shibata et al, 1999(Shibata et al, , 2000Navajas-Perez et al, 2005;Cunado et al, 2007).…”

Comparative Genetic Mapping Points to Different Sex Chromosomes in Sibling Species of Wild Strawberry (Fragaria)

“…Furthermore, sex chromosomes have diverged within one section of the genus, with species Silene diclinis possessing neo-sex chromosomes, while two sister species (S. latifolia and S. dioica) have only the ancestral state (Howell et al 2009). Despite the wide phylogenetic distribution of dioecy and sex chromosomes in flowering plants (Charlesworth 2002), only a handful have been the subject of genetic mapping studies (grape: Telgmann-Rauber et al 2007; papaya: Sondur et al 1996;Ma et al 2004;Chen et al 2007; kiwifruit: Testolin et al 2001), and even fewer have been the subject of comparative analyses that can inform on other evolutionary dynamics (e.g., Rumex: Navajas- Perez et al 2005;Cunado et al 2007; Silene: Howell et al 2009;papaya: Yu et al 2008a;Wu et al 2010).…”