Plant Genome IV Conference Plant Genome IV Conference
We have initiated "single-pass" sequencing of loblolly pine cDNAs to provide molecular tools for studying conifer genome organization and evolution. We have sequences from approximately 200 seedling cDNAs and have initiated projects for additional tissues. Based on comparisons to sequences in electronic databases, we can assign tentative identities to approximately 30% of these cDNAs. Most of the identified cDNAs from seedlings encode cellular metabolism enzymes and structural proteins. Significant numbers of cDNAs reveal complex gene families on southern blots (Sewell et al., this meeting). Identities based on sequence similarity confirm that specific genes which appear single or low copy in angiosperms are complex in pines. We do not know whether functional gene copies have been amplified. Reverse transcription of host cellular mRNAs to form pseudogenes is one possible mechanism by which complex conifer gene families may have arisen. Pine genomes harbor large numbers (~100,000 in pines) of a retrotransposable element, IFG. Although IFG family members appear to be widely dispersed within pine genomes, we have preliminary evidence that individual elements can be found closely linked (within 10 kilobases) to members of the complex alcohol dehydrogenase family. We are investigating the possible association of IFG elements with other pine genes. Finally, we have evidence that one or more IFG elements are transcribed and thus may continue to replicate new retrotransposons.