Ogre retrotransposons in Lathyrus species

A repeated DNA element (pLsat10) 225 bp in length, whose nucleotide sequence was partly identical to that of the PBS of Ogre retrotransposons in Pisum sativum and in part 78.3% similar to that of the adjoining portion of the 50 LTR of these retroelements, was isolated from a partial genomic library of Lathyrus sativus. By using this DNA sequence in dot-blot and Southern blot hybridizations, Ogre retrotransposons were traced and studied in four Lathyrus species (L. latifolius, L. odoratus, L. sativus, and L. sylvestris). The copy number per ng of DNA of pLsat-related sequences in L. sativus turned out to be 1.56107, and an upper limit estimate of the proportion of the genome made up by Ogre may be 10–16%. The results of Southern blot hybridization of pLsat10 to genomic DNAs indicated the occurrence, in each Lathyrus genome, of distinct subfamilies of Ogre and suggested a higher activity of these retrotransposons in annual than in perennial species. Fluorescent in situ hybridization of pLsat10 showed Ogre to be widely dispersed in all chromosomes, but poorly represented or absent in heterochromatic chromosome regions.