Diversity and evolution of Ty1- copia and Ty3- gypsy retroelements in the non-photosynthetic flowering plants Orobanche and Phelipanche (Orobanchaceae)

Abstract

We present the first study on the diversity and evolution of Ty1- copia and Ty3- gypsy retroelements in a group of non-photosynthetic flowering plants. To this end partial sequences of the reverse transcriptase ( rt) gene were obtained from 20 clones for each retroelement type from seven and six accessions of Orobanche and Phelipanche (Orobanchaceae), respectively. Overall sequence similarity is higher in Ty3- gypsy elements than in Ty1- copia elements in agreement with the results from other angiosperm groups. Higher sequence diversity and stronger phylogenetic structure, especially of Ty1- copia sequences, in Orobanche species compared to Phelipanche species support the previously suggested hypothesis (based on karyological and cytological data) that genomes of Orobanche species are more dynamic than those of Phelipanche species. No evidence was found for intraspecific differences of retroelement diversity nor for differences between pest taxa and their putative wild relatives, e.g., O. crenata and O. owerini. The occurrence of a few sequences from Phelipanche species in clades otherwise comprising sequences from Orobanche species might be due to horizontal gene transfer, but the alternative of vertical transmission cannot be rejected unambiguously.