Hairpins involving both inverted and direct repeats are associated with homoplasious indels in non-coding chloroplast DNA of Taraxacum (Lactuceae: Asteraceae)

Sequence variation in 2.2 kb of non-coding regions of the chloroplast genome of eight dandelions (Taraxacum: Lactuceae) from Asia and Europe is interpreted in the light of the phylogenetic signal of base substitutions vs. indels (insertions-deletions). The four non-coding regions displayed a total of approximately 30 structural mutations of which 9 are potentially phylogenetically informative. Insertions, deletions, and an inversion were found that involved consecutive stretches of up to 172 bases. When compared to phylogenetic relationships of the chloroplast genomes based on nucleotide substitutions only, many homoplasious indels (33%) were detected that differed considerably in length and did not comprise simple sequence repeats typically associated with replication slippage. Though many indels in the intergenic spacers were associated with direct repeats, frequently, the variable stretches participated in inverted repeat stabilized hairpins. In each intergenic spacer or intron examined, nucleotide stretches ranging from 30 to 60 bp were able to fold into stabilized secondary structures. When these indels were homoplasious, they always ranked among the most stabilized hairpins in the non-coding regions. The association of higher order structures that involve both classes of repeats and parallel structural mutations in hot spot regions of the chloroplast genome can be used to differentiate among mutations that differ in phylogenetic reliability.