Nucleotide variation and secondary structures of nuclear ribosomal ITS2 in phylogeny relationships of some wheat species

Abstract

This research aimed to estimate the nucleotide polymorphism and point mutation/substitutions for ITS2 region in 12 different Triticum and Aegilops species, and to demonstrate their phylogenetic relationships. The aligned ITS2 dataset showed a total of 67 SNPs and transitions (75%) predominant over transversions (25%). The C/T transitions were observed at highest level in the studied species. The highest nucleotide substitutions occurred in ITS2 sequences of T. aestivum, T. turgidum, and A. speltoides that showed similar substitutions on the base sites 76, 193, 215, 230 and 241 (TCCAG changed to ATTTA). T. boeticum and T. urartu showed similar substitutions on the base sites 85, 201, 231, 234 and 252 (GTGCC changed to AGATA). Remarkably, the nucleotide of base site 146 was C in all Triticum species, but T in all Aegilops species. The substitution rate in A. neglecta, and A. umbellulata was zero, it was concluded that their ITS2 is conserved. The secondary structures of ITS2 in the studied species was similar to that of the other flowering plants with four helices and the variation in helices length. The helix III had the longest length compared to the other helices. The length ranges of helices I, II, IV varied from 9 (T. turgidum, and T. urartu) to 10, 11 (A. cylindrica) 13 and 6 (A. speltoides) and 10 (T. boeticum) paired bases, respectively. Using pairwise ITS2 nucleotide comparisons, the closeness of A. caudata with A. cylindrica, T. boeticum with T. urartu, A. neglecta with A. umbellulata was observed. Phylogeny trees classified 12 species into four main clades. The highest point mutations occurred in ITS2 sequences related to the species grouped in the first clade.