Evolution and origin of polyploid Triticeae (Poaceae) revealed through the nuclear pgk1 gene

Abstract

Despite many studies on the taxonomy of the Triticeae, no general consensus has yet been agreed upon as to their phylogenetics. This is attributed to extremely high rates of hybridization and polyploidization. Levels of nucleotide divergence provide key evidence in to the evolution of polyploids. The pgk1 gene was used to investigate the potential evolutionary dynamics of the Triticeae, and phylogenetic analyses (Maximum Parsimony and Neighbor-Joining) were carried out to determine the diploid origin of polyploids within the tribe in relation to their A[superscript u], B, D, St, Ns, P, and H haplomes. Origins of the A[superscript u], B, and D genomes were linked to Triticum urartu, Aegilops speltoides, and Aegilops tauschii respectively. Putative St genome donor was Pseudoroegneria, while Ns and P donors were Psathyrostachys and Agropyron. H genome diploid donor is Hordeum. Highly negative and significant Tajima’s D values for the St, A[superscript u], and D genomes along with high rates of polymorphisms and low sequence diversity correlate with purifying selection pressures within the polyploid members of the tribe, acting to conserving homologous copies of pgk1 from each diploid origin. Nucleotide diversity values varied, indicating different selective pressures on each species within the tribe, and fortifying their identification as separate species.