Co-evolution of plant LTR-retrotransposons and their host genomes EVIEW R

Transposable elements (TEs), particularly, long terminal repeat retrotransposons (LTR-RTs), are the most abun- dant DNA components in all plant species that have been investigated, and are largely responsible for plant genome size variation. Although plant genomes have experi- enced periodic proliferation and/or recent burst of LTR- retrotransposons, the majority of LTR-RTs are inactivated by DNA methylation and small RNA-mediated silencing mechanisms, and/or were deleted/truncated by unequal homologous recombination and illegitimate recombina- tion, as suppression mechanisms that counteract genome expansion caused by LTR-RT amplifi cation. LTR-RT DNA is generally enriched in pericentromeric regions of the host genomes, which appears to be the outcomes of pref- erential insertions of LTR-RTs in these regions and low effectiveness of selection that purges LTR-RT DNA from these regions relative to chromosomal arms. Potential functions of various TEs in their host genomes remain blurry; nevertheless, LTR-RTs have been recognized to play important roles in maintaining chromatin structures and centromere functions and regulation of gene expres- sions in their host genomes.