A Chloroplast DNA Inversion Marks an Ancient Evolutionary Split in the Sunflower Family (Asteraceae)

We determined the distribution of a chloroplast DNA inversion among 80 species representing 16 tribes of the Asteraceae and 10 putatively related families. Filter hybridizations using cloned chloroplast DNA restriction fragments of lettuce and petunia revealed that this 22-kilobase-pair inversion is shared by 57 genera, representing all tribes of the Asteraceae, but is absent from the subtribe Barnadesiinae of the tribe Mutisieae, as well as from all families allied to the Asteraceae. The inversion thus defines an ancient evolutionary split within the family and suggests that the Barnadesiinae represents the most primitive lineage in the Asteraceae. These results also indicate that the tribe Mutisieae is not monophyletic, since any common ancestor to its four subtribes is also shared by other tribes in the family. This is the most extensive survey of the systematic distribution of an organelle DNA rearrangement and demonstrates the potential of such mutations for resolving phylogenetic relationships at higher taxonomic levels.