Studied on gypsy-type retrotransposons in plant ; their stuructural diversity and their choromosomal localization

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Phylogenetic analysis of the rt genes of gypsy-type retrotransposons from rice (RIRE3, RIRE8 and RIRE2) as well as various plants (monocots, dicots, pine, ginkgo, horsetail, liverwort and algae) showed that these retrotransposon homologues could be classified into two families, in each of which, they were further classified into several subfamilies. This indicates that sequence divergence during vertical transmission has been a major influence on the evolution of gypsy-type retrotransposons in plants. An another rice gypsy-type retrotranson, named RIRE7, is a retrotransposon wigh homology to several DNA segaments present in the centromere regions of cereal chromosomes. RIRE7 were also found to be inserted into a site within a tandem repeat sequence with a unit length of 155bp, named TrsD. FISH analysis of the metaphase chromosomes of *. sativa showed that both RIRE7 and TrsD sequences were present in the centromere region of the chromosomes. Further FISH analysis of rice pachytene chromosomes showed that the TrsD sequences were located in a pericentromeric heterochromatin region. These findings strongly sugge that RIRE7, as well as TrsD, is an important component of the pericentromeric heterochromatin of rice chromosomes.