Plant & Animal Genomes XV Conference Plant & Animal Genomes XV ConferenceJanuary 13-17, 2007
Town & Country Convention Center
San Diego, CA
Polyploidy is a prevalent form of genome evolution, particularly among angiosperms where polyploidy accounts for at least 2-4% of speciation events. Recent analyses of angiosperm genomes have identified numerous ancient polyploid events, or paleopolyploidy, and implicate polyploidy in the ancestry of nearly all angiosperms. However, these analyses failed to identify paleopolyploidy in members of the Compositae, a family that contains approximately 10% of angiosperm species and hypothesized paleopolyploidy based on phylogenetic chromosome number variation. In the present analysis, the age distribution of duplicate gene pairs was examined for evidence of paleopolyploidy in 10 Compositae Genome Project EST libraries for five species each of Helianthus and Lactuca. Evidence for paleopolyploidy was observed in both genera. In Helianthus, evidence for a paleopolyploid event centered at approximately Ks = 0.5 was common to all species analyzed, and supports paleopolyploid hypotheses for the origin of the Heliantheae s.l. + Eupatorieae, a clade that contains 2.5% of angiosperm species. An apparent genome doubling event was also observed among all species of Lactuca centered at Ks = 0.8. A peak consistent with an older, second paleopolyploid event was also observed at Ks = 1.4 in four of the five Lactuca species. These results suggest that polyploidy has played a role in Compositae evolution, and implicate polyploidy in the ancestry of a significant percentage of angiosperms. Ongoing work to analyze additional Compositae EST libraries will provide further time points for the estimation of paleopolyploidy across the Compositae.