title: Molecular cytogenetics (FISH, GISH) of Coccinia grandis : a ca. 3 myr-old species of cucurbitaceae with the largest Y/autosome divergence in flowering plants.
abstract: The independent evolution of heteromorphic sex chromosomes in 19 species from 4 families of flowering plants permits studying X/Y divergence after the initial recombination suppression. Here, we document autosome/Y divergence in the tropical Cucurbitaceae Coccinia grandis, which is ca. 3 myr old. Karyotyping and C-value measurements show that the C. grandis Y chromosome has twice the size of any of the other chromosomes, with a male/female C-value difference of 0.094 pg or 10% of the total genome. FISH staining revealed 5S and 45S rDNA sites on autosomes but not on the Y chromosome, making it unlikely that rDNA contributed to the elongation of the Y chromosome; recent end-to-end fusion also seems unlikely given the lack of interstitial telomeric signals. GISH with different concentrations of female blocking DNA detected a possible pseudo-autosomal region on the Y chromosome, and C-banding suggests that the entire Y chromosome in C. grandis is heterochromatic. During meiosis, there is an end-to-end connection between the X and the Y chromosome, but the X does not otherwise differ from the remaining chromosomes. These findings and a review of plants with heteromorphic sex chromosomes reveal no relationship between species age and degree of sex chromosome dimorphism. Its relatively small genome size (0.943 pg/2C in males), large Y chromosome, and phylogenetic proximity to the fully sequenced Cucumis sativus make C. grandis a promising model to study sex chromosome evolution.
authors.affiliation: Systematic Botany and Mycology, University of Munich (LMU), Munich, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Sousa
authors.forename: J
authors.initials: J
authors.lastname: Fuchs
authors.forename: S S
authors.initials: SS
authors.lastname: Renner
mesh_terms: D002871:Chromosome Banding; D032461:Chromosomes, Plant / Q000235:genetics*; D019662:Cucurbitaceae / Q000235:genetics*; D020732:Cytogenetic Analysis / Q000379:methods*; D018744:DNA, Plant / Q000235:genetics; D004275:DNA, Ribosomal / Q000235:genetics; D014644:Genetic Variation; D017404:In Situ Hybridization, Fluorescence / Q000379:methods; D059785:Karyotype; D008540:Meiosis / Q000235:genetics; D008938:Mitosis / Q000235:genetics
chemical_list: D018744:DNA, Plant; D004275:DNA, Ribosomal