Fluorescent in situ Hybridization Analysis of Penelope-like Elements in Southern Yellow Pine Tree Genomes

We have recently discovered that retrotransposons belonging to the group of Penelope-like elements (PLEs) have been transferred from insects to a common ancestor of conifers ~340 million years ago. Approximately 145,000 of these conifer elements, which we called Dryads, have been identified in the loblolly pine (Pinus taeda L.) genome assembly. Preliminary fluorescent in situ hybridization (FISH) analyses have shown that Dryad sequences belonging to the PtRPX_125 family are interspersed across loblolly pine chromosomes. To further investigate the chromosomal distribution of Dyads among conifers we performed FISH experiments on the three other Southern pine tree species, viz., slash pine (Pinus elliottii), longleaf pine (Pinus palustris), and shortleaf pine (Pinus echinata). We found that the chromosomal localization of PtRPX_125 sequences is largely comparable between these pine species, suggesting that this family has been largely inactive since their separation 5-15 million years ago, or that few insertions of PtRPX_125 elements have accumulated in the recent past in these genomes.