LTR-retrotransposons as major drivers of genome diversification across the genus Helianthus L.

Transposons play a key role in the evolution of species leading to rapid genome remodeling. Herein, we study the variability of the repetitive fraction of the genome in the genus Helianthus which recently has emerged as model for studying the genetics of speciation and adaptation. After determining the relative genome size of ten species and one subspecies of Helianthus, different assembling and clustering approaches were carried on by using next generation sequencing techniques to explore the repetitive component of the genomes. On average, repetitive DNA in Helianthus species represented more than 75% of the genome, with long terminal repeat retrotransposons (LTRREs) being the vast majority of repetitive sequences. Prevalence of Gypsy over Copia superfamily was observed; and, among Gypsy lineages, Chromovirus was by far the most represented in each analyzed species. Moreover, considerable variability in the abundance of diverse LTR-RE lineages was found across the genus, showing differences especially between annual and perennial species. In some cases, such variation produced relevant effects on species genome size which was only partly related to the ploidy level.