Submitted to: Plant Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2001
Publication Date: 2/10/2002
Citation: Huang, S., Sirikhachornkit, A., Faris, J.D., Su, X., Gill, B.S., Haselkorn, R., Gornicki, P. 2002. Phylogenetic analysis of the acetyl-coa carboxylase and 3-phosphoglycerate kinase loci in wheat and other grasses. Plant Molecular Biology 48:805-820. Interpretive Summary: Common bread wheat is one of the worlds most important crops, and it has a relatively complex genome compared to other crop species. Wheat evolved through the convergence of three ancestral grass species with relatively simple genomes. In recent decades, wheats progenitor species have been identified through various studies. We examined the DNA sequences of acetyl-CoA carboxylase (ACCase) and two forms of 3-phosphoglycerate kinase (PGK) genes in wheat and some of its relatives to study grass evolution. Relationships among plant ACCase and PGK genes, revealed by their gene sequences, were found to be consistent with the known facts of their evolution: the ACCase gene arose by duplication of a different but related form of another ACCase gene, and one of the PGK genes was of prokaryotic origin. Construction of evolutionary trees indicated that primitive wheats diverged from Lolium at 35 million years ago (MYA), from barley at 11 MYA, and from rye at 7 MYA. The gene duplication event leading to the ACCase gene in grasses occurred at 129 MYA. Divergence of one form of PGK genes between grasses and dicots occurred at 137 MYA, while the other form of PGK genes diverged between grasses and dicots at 155 MYA. These studies also indicated that the first bread wheats arose about 8 thousand years ago, and primitive durum wheats arose about 0.5 MYA. These genes provided a well understood system for studying the evolution of grasses.
Technical Abstract: We have applied a two-gene system based on sequence of nuclear genes encoding multi-domain plastid acetyl-CoA carboxylase (ACCase) and plastid 3-phosphoglycerate kinase (PGK) to study grass evolution. Our analysis revealed single-copy nature of these genes in most of the studied grass species allowing the establishment of orthologous relationships between them. Relationships among plant multi-domain ACCases and PGKs, revealed by their gene sequences, are consistent with the known facts of their evolution: the eukaryotic origin of the plastid ACCase, created by duplication of a gene encoding cytosolic multi-domain ACCase gene early in grass evolution, and the prokaryotic (endosymbiont) origin of the plastid PGK. The major phylogenetic relationships among grasses deduced from nucleotide sequence comparisons of ACCase and PGK genes are consistent with each other and with the milestones of grass evolution revealed by other methods. Nucleotide substitution rates were calculated based on multiple pairwise sequence comparisons. On a relative basis, with the divergence of the Pooideae and Panicoideae subfamilies set at 60 million years ago (MYA), events leading to the Triticum/Aegilops complex occurred at the following intervals: divergence of Lolium (Lolium rigidum) at 35 MYA, divergence of Hordeum (Hordeum vulgare) at 11 MYA and divergence of Secale (Secale cereale) at 7 MYA. On the same scale, gene duplication leading to the multi-domain plastid ACCase in grasses occurred at 129 MYA, divergence of grass and dicot plastid PGK genes at 137 MYA, and divergence of grass and dicot cytosolic PGK genes at 155 MYA. The ACCase and PGK genes provide a well-understood two-locus system to study grass phylogeny, evolution and systematics.