3 years ago

The fate of ribosomal RNA genes in spontaneous polyploid dogrose hybrids (Rosa L. sect. Caninae (DC.) Ser.) exhibiting non-symmetrical meiosis

Susan Lippitsch, Aleš Kovařík, Marco Groth, Christiane M. Ritz, Jana Lunerová, Veit Herklotz
Dogroses represent an exceptional system for studying the effects of genome doubling and hybridization: their asymmetrical meiosis enables recombination in bi-parentally inherited chromosomes but prevents it in maternally inherited ones. We employed fluorescent in situ hybridization, genome skimming, amplicon sequencing of genomic and cDNA as well as conventional cloning of nuclear ribosomal DNA in two phylogenetically distinct pentaploid (2n = 5x = 35) species, Rosa canina and R. inodora, and their naturally occurring reciprocal hybrids, R. dumalis (5x) and R. agrestis (5x, 6x). Both progenitor species differed in composition, meiotic behaviour and expression of rDNA loci: R. canina (five 18S and 5–8 5S loci) was dominated by the Canina ribotypes but R. inodora (four 18S loci and 7–8 5S loci) by the Rubiginosa ribotype. The co-localised 5S/18S loci occurred on either bivalent-forming (R. canina) or univalent-forming (R. inodora) chromosomes. Ribosomal DNA loci were additively inherited, however, the Canina ribotypes were dominantly expressed, even in genotypes with relatively low copy number of these genes. Moreover, we observed rDNA homogenization towards the paternally transmitted Canina ribotype in 6x R. agrestis. The here observed variation in arrangement and composition of rDNA types between R. canina and R. inodora suggests involvement of different genomes in bivalent formation. We hypothesize that the asymmetrical meiosis arose at least twice by independent ancient hybridization events. This article is protected by copyright. All rights reserved.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1111/tpj.13843

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