title: Structural polymorphisms and distinct genomic composition suggest recurrent origin and ongoing evolution of B chromosomes in the Prospero autumnale complex (Hyacinthaceae).
abstract: Supernumerary B chromosomes (Bs) are genomic parasitic components, originating from the A complement via chromosomal rearrangements, which follow their own evolutionary trajectories. They often contain repetitive DNAs, some shared with regular chromosomes and some newly evolved. Genomic composition, origin and evolution of Bs have been analysed in the chromosomally variable Prospero autumnale complex. Two rDNAs and a satellite DNA (PaB6) from regular chromosomes were mapped to Bs of 26 plants from three diploid cytotypes, their hybrids and polyploid derivatives. In homoploid diploid hybrids, genomic in situ hybridization (GISH) allowed B painting with the parental DNAs. Bs were structurally variable and highly enriched in 5S rDNA and satDNA PaB6, and rarely in 35S rDNA. Eleven combinations of rDNA and PaB6 localization were observed. The quantities of PaB6 in Bs and regular chromosomes were not correlated, suggesting amplification mechanisms other than recombination. PaB6 and 5S rDNA amounts increased with increasing ploidy level. GISH revealed two independent origins of Bs. The structural variation, repeat content, repeat-type fluctuations and differing genomic affinities of Bs in different cytotypes suggest that they represent young proto-B chromosomes. Bs in P. autumnale probably form recurrently as by-products of the extensive genome restructuring within this chromosomally variable species complex.
authors.affiliation: Department of Botany and Biodiversity Research, University of Vienna, Rennweg 14, A-1030, Vienna, Austria.
authors.forename: Tae-Soo
authors.initials: TS
authors.lastname: Jang
authors.affiliation: Cambridge University Botanic Garden, Cambridge, CB2 1JF, UK.
authors.forename: John S
authors.initials: JS
authors.lastname: Parker
authors.affiliation: Department of Botany and Biodiversity Research, University of Vienna, Rennweg 14, A-1030, Vienna, Austria.
authors.forename: Hanna
authors.initials: H
authors.lastname: Weiss-Schneeweiss
mesh_terms: D000070357:Asparagaceae / Q000235:genetics*; D005075:Biological Evolution; D032461:Chromosomes, Plant / Q000235:genetics*; D004275:DNA, Ribosomal / Q000235:genetics; D004276:DNA, Satellite / Q000235:genetics; D004171:Diploidy; D018745:Genome, Plant; D017404:In Situ Hybridization, Fluorescence; D008540:Meiosis / Q000235:genetics; D011110:Polymorphism, Genetic; D011123:Polyploidy; D020080:Tandem Repeat Sequences / Q000235:genetics
chemical_list: D004275:DNA, Ribosomal; D004276:DNA, Satellite
keywords: B-chromosome evolution; B-chromosome painting; Prospero autumnale complex; fluorescence in situ hybridization (FISH); genomic in situ hybridization (GISH); polyploids; rDNA (5S and 35S rDNA); satellite DNA PaB6