Variation of rDNA loci of polyploid Solanum elaeagnifolium (Solanaceae)

Abstract

Fluorescence in situ hybridization (FISH) was applied to detect gene rearrangements and genome downsizing in Solanum elaeagnifolium, an invasive weed with 2n = 24, 48 and 72 populations. The probes employed were pTa71 containing the 18S5.8S26S gene, and a 5S rDNA probe obtained from S. stuckertii. As a result, diploids presented a pair of 18S5.8S26S signals and a pair of 5S, whereas tetra- and hexaploids increased their FISH marks proportional to the ploidy level. In all cases, rDNA loci were non-syntenic, and position was conserved along the polyploid series. The cytotypes would have formed recently and drastic rearrangements have not yet occurred. However, in each cell of the 4x and 6x individuals, signal intensity in one locus of the 18S5.8S26S was stronger, suggesting a potential loss of copies in the remaining loci. In addition, one hexaploid showed an extra 5S signal in heterozygosis. The data obtained suggest a recent, recurrent autopolyploidy.