Genome evolution in alpine oat-like grasses through homoploid hybridization and polyploidy

• Published in: AoB plants Vol. 8
• Main Authors: Winterfeld, Grit, Wölk, Alexandra, Röser, Martin
• Format: Journal Article
• Language: English
• Published: England Oxford University Press 01-01-2016
• Subjects: Chromosomes; Diploids; DNA probes; Fluorescence in situ hybridization; Genomes; Helictotrichon; Hybridization; Hybrids; Karyotypes; Nucleotide sequence; Phylogeny; Polyploidy; Satellite DNA; Speciation; Species; Alps; Alps; karyotype; polyploidy; Helictotrichon; Poaceae; hybridization; Topoisomerase VI
• ISSN: 2041-2851; 2041-2851
• DOI: 10.1093/aobpla/plw039

Molecular cytogenetic and phylogenetic analysis of alpine endemic wild oats of genus Helictotrichon represents a remarkable example of speciation and diversification through homoploid hybridisation and polyploidisation. Results suggest a primary centre of species establishment in the eastern regions of the Alps, with the westward expansion and subsequent ice age interruption resulting in a recently disjunct distribution between populations of the southwestern and southeastern Alps.
Hybridization and polyploidization can radically impact genome organization from sequence level to chromosome structure. As a result, often in response to environmental change and species isolation, the development of novel traits can arise and will tend to result in the formation of homoploid or polyploid hybrid species. In this study we focus on evidence of hybridization and polyploidization by ascertaining the species parentage of the endemic alpine Helictotrichon parlatorei group. This group comprises five taxa; the diploids H. parlatorei, Helictotrichon setaceum subsp. setaceum and subsp. petzense, their putative hybrid Helictotrichon ×krischae and the hexaploid Helictotrichon sempervirens. For molecular analyses, cloned nuclear Topoisomerase VI genes of H. sempervirens and H. ×krischae were sequenced and compared with sequences of the diploids to estimate the evolutionary history in this group. In addition, detailed chromosome studies were carried out including fluorescence in situ hybridization (FISH) with 5S and 45S ribosomal and satellite DNA probes, and fluorochrome staining with chromomycin and DAPI. Two distinct types of Topoisomerase VI sequences were identified. One of them (SET) occurs in both subspecies of H. setaceum, the other (PAR) in H. parlatorei. Both types were found in H. ×krischae and H. sempervirens. Karyotypes of H. parlatorei and H. setaceum could be distinguished by chromosomes with a clearly differentiated banding pattern of ribosomal DNAs. Both patterns occurred in the hybrid H. ×krischae. Hexaploid H. sempervirens shares karyotype features with diploid H. parlatorei, but lacks the expected chromosome characteristics of H. setaceum, possibly an example of beginning diploidization after polyploidization. The geographic origin of the putative parental species and their hybrids and the possible biogeographical spread through the Alps are discussed.