Evolutionary dynamics of transposable elements and satellite DNAs in polyploid Spartina species
Leitch, Andrew R.
Leitch, Ilia J.
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Repeated sequences and polyploidy play a central role in plant genome dynamics. Here, we analyze the
evolutionary dynamics of repeats in tetraploid and hexaploid Spartina species that diverged during the last 10
million years within the Chloridoideae, one of the poorest investigated grass lineages. From high-throughput
genome sequencing, we annotated Spartina repeats and determined what sequence types account for the
genome size variation among species. We examined whether differential genome size evolution correlated with
ploidy levels and phylogenetic relationships. We also examined the tempo of repeat sequence dynamics associated
with allopatric speciation over the last 3–6 million years between hexaploid species that diverged on the
American and European Atlantic coasts and tetraploid species from North and South America. The tetraploid
S. spartinae, whose phylogenetic placement has been debated, exhibits a similar repeat content as hexaploid
species, suggesting common ancestry. Genome expansion or contraction resulting from repeat dynamics seems to
be explained mostly by the contrasting divergence times between species, rather than by genome changes
triggered by ploidy level change per se. One 370 bp satellite may be exhibiting ‘meiotic drive’ and driving
chromosome evolution in S. alterniflora. Our results provide crucial insights for investigating the genetic and
epigenetic consequences of such differential repeat dynamics on the ecology and distribution of the meso- and
neopolyploid Spartina species.