Plant & Animal Genome VI Conference

W33

HIGH COPY RETROTRANSPOSONS IN PINE GENOMES: EVIDENCE FOR ACTIVE COPIES

1. Institute of Forest Genetics, USDA Forest Service, PO Box 245, Berkeley, CA 94701
2. Department of Soil and Crop Sciences, Texas A and M University, College Station, TX 77843

Recent evidence (SanMiguel et al., 1996) suggests that more than 50% of large plant genomes such as corn may be retrotransposons. Such high copy numbers for retrotransposons in plant genomes suggests that these virus-like sequences may have had a strong impact on plant genome evolution. Pine genomes are large and contain many repetitive sequences, including retrotransposons of both the Ty1 (Kamm et al., 1996) and Ty3 classes. We have studied the wide distribution of Ty3-like retrotransposons in conifer genomes. Sequence polymorphisms among sub-classes of the large Ty3 family of pine retrotransposons reflects a pattern of sequence mutation and re-amplification of different retrotransposons. In situ hybridization demonstrates a highly dispersed organization for both Ty1- and Ty3-type retrotransposons. The very high copy number of pine retrotransposons suggests significant reverse transcription and replication of new elements during the evolution of pine species. We have evidence that at least some of the Ty3-type of pine retrotransposons remain transcriptionally active.