XVI International Botanical Congess

Although most seed plants lack any intron in the mitochondrial coxI gene, a group I intron, homologous with the mobile ai4 intron in yeast, occurs sporadically in angiosperms. PCR tests (>300 species) found the intron to be rare in basal angiosperms, monocots, and basal eudicots, but more common in Asteridae and Rosidae. We compared coxI exon trees with intron trees to test hypotheses of ancestral intron vs. recent intron acquisition(s) in angiosperms. Recent initial invasion(s), followed by verticalCand many horizontalCtransmissions of the intron were inferred across distantly related angiosperm groups. Surprisingly, the intron is found in every independently-evolved (nonphotosynthetic) parasitic plant lineage. We are investigating the possibility of direct host-parasite or parasite-host intron transfer as a mechanism to explain some of the extreme horizontal gene flow shown by this unique parasitic DNA element.