A comparative phenotypic and ITS based genotypic study in thyme species (Thymus L. Lamiaceae)

In this study, the internal transcribed spacers (ITS), ITS1 and ITS2, of nuclear ribosomal DNA of Thymus daenensis subsp. daenensis, Th. persicus, Th. pubescens and Th. trautvetteri (Lamiaceae) which were collected from different locations from Azarbaijan province of Iran were PCR-amplified, sequenced and compared with ITS sequences of other thyme species. Sequences from the endogenous species had high G+C contents (58–64%) and low free energy (ΔG) values (as low as -106.20), ensuring a higher stability of the secondary structures in the ITS1 and ITS2 regions. ITS1 and ITS2 region lengths ranged from 220 to 236 bp. Our findings showed two main clades in the strict consensus phylogenetic tree, confirming difference existing in the secondary structure of the ITS1 of the sequences reported in this study and that of previously reported ones. Although this study showed that thyme species in Azarbaijan province had identical ITS sequences, they possessed different morphologies. A comparison between the sequences obtained in this study and thyme GenBank accessions showed five insertions-deletions (indels) and sixteen substitutions. This study suggests that these species might be recent derivatives of their ancestor.