XVI International Botanical Congess

Gossypium omega-6 fatty acid desaturases are encoded by a small multigene family. One gene (ghFAD2-1) contains a ca 1100 bp intron located in the 5' untranslated region. Phylogenetic analyses of the intron sequences from 31 species demonstrate that the two allotetraploid genes are orthologs derived from their A- and D-genome diploid progenitors. The D diploid introns are accumulating substitutions faster than the A diploid introns. This difference is greater in the allotetraploid species. Comparison of ghFAD2-1 gene topologies with other gene topologies suggests that G. bickii experienced two homoploid reticulate events, one involving the nuclear 18S-26S rDNA, the other the chloroplast genome. The 12 Kimberley (Australia) species share a common ancestor but diverged into a lineage of coastal species and a lineage of inland species.