Significant Expansion of Vicia pannonica Genome Size Mediated by Amplification of a Single Type of Giant Retroelement

Amplification and eventual elimination of dispersed repeats, especially those of the retroelement origin, account for most of the profound size variability observed between plant genomes. In most higher plants investigated so far, differential accumulation of various families of elements contribute to these differences. Here we report the identification of giant Ty3/gypsy-like retrotransposons from the legume plant Vicia pannonica, which alone makes up about 38% percent of this species genome. These retrotransposons have structural features of the Ogre elements previously identified in the genomes of pea and Medicago. These features include extreme size (25 kb), presence of an extra ORF upstream of gag-pol region, and a putative intron dividing the prot and rt coding sequences. The Ogre elements are evenly dispersed on V. pannonica chromosomes except for terminal regions containing satellite repeats, their individual copies show extraordinary sequence similarity, and at least part of them are transcriptionally active which suggests their recent amplification. Similar elements were also detected in several other Vicia species but in most cases in significantly lower numbers. However, there was no obvious correlation of the abundance of Ogre sequences with the genome size of these species.

Key Words: LTR retrotransposon, Ogre elements, Vicia, genome size, plant genome evolution

Online ISS 1091-6490
Copyright 2008 by the Genetics Society of America
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