Large vs small genomes in Passiflora: the influence of the mobilome and the satellitome

Abstract

While two lineages of retrotransposons were more abundant in larger Passiflora genomes, the satellitome was more diverse and abundant in the smallest genome analysed. Repetitive sequences are ubiquitous and fast-evolving elements responsible for size variation and large-scale organization of plant genomes. Within Passiflora genus, a tenfold variation in genome size, not attributed to polyploidy, is known. Here, we applied a combined in silico and cytological approach to study the organization and diversification of repetitive elements in three species of this genus representing its known range in genome size variation. Sequences were classified in terms of type and repetitiveness and the most abundant were mapped to chromosomes. We identified long terminal repeat (LTR) retrotransposons as the most abundant elements in the three genomes, showing a considerable variation among species. Satellite DNAs (satDNAs) were less representative, but highly diverse between subgenera. Our results clearly confirm that the largest genome species (Passiflora quadrangularis) presents a higher accumulation of repetitive DNA sequences, specially Angela and Tekay elements, making up most of its genome. Passiflora cincinnata, with intermediate genome and from the same subgenus, showed similarity with P. quadrangularis regarding the families of repetitive DNA sequences, but in different proportions. On the other hand, Passiflora organensis, the smallest genome, from a different subgenus, presented greater diversity and the highest proportion of satDNA. Altogether, our data indicates that while large genomes evolved by an accumulation of retrotransposons, the smallest genome known for the genus has evolved by diversification of different repeat types, particularly satDNAs.

Keywords: Chromosome evolution; Genome skimming; NGS; Passion-fruit; Retrotransposons; SatDNA.