Submitted to: Proceedings of the National Academy of Sciences
Publication Type: Proceedings
Publication Acceptance Date: 2/20/2002
Publication Date: 7/13/2002
Citation: Huang, S., Sirikhachornkit, A., Su, X., Faris, J.D., Gill, B., Haselkorn, R., Gornicki, P. 2002. Genes encoding plastid acetyl-coa carboxylase and 3-phosphoglycerate kinase of the triticum/aegilops complex and the evolutionary history of polyploid wheat. Proceedings of the National Academy of Sciences WA 99:8133-8138. Interpretive Summary: Common bread wheat is one of the world's 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, wheat's 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. 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 diploid progenitors of polyploid wheat radiated from a common ancestor 2.5-4.5 MYA. The formation of tetraploid ancestors of durum wheat formed less than 0.5 MYA.These studies also indicated that the first bread wheats arose about 8 thousand years ago. The origin of the B genome remains unkown. These genes provided a well-understood system for studying the evolution of grasses.
Technical Abstract: The classic wheat evolutionary history is one of adaptive radiation of the diploid Triticum/Aegilops species (A, S, D) , genome convergence and divergence of the tetraploid (T. turgidum AABB, and T. timopheevii AAAGG) and hexaploid (T. aestivum, AABBDD) species. The objective of this study was to analyze Acc-1 (plastid acetyl-CoA carboxylase) and Pgk-1 (plastid 3-phosphoglycerate kinase) genes to determine phylogenetic relationships among Triticum and Aegilops species of the wheat lineage and to establish the timeline of wheat evolution based on gene sequence comparisons. Our analysis confirmed T. urartu as the A genome donor of tetraploid and hexaploid wheats. We further show that the A genome of polyploid wheat diverged from T. urartu less then half a million years ago (MYA), indicating a relatively recent origin of polyploid wheat. The D genome sequences of T. aestivum and Ae. taushii were identical. T. aestivum arose from hybridization of T. turgidum and Ae. tauschii only 8,000 years ago. The diploid Triticum and Aegilops progenitors of the A, B, D, G and S genomes all radiated 2.5-4.5 MYA. Our data suggest that Acc-1 and Pgk-1 loci have different histories in different lineages, indicating genome mosaicity and significant intra-specific differentiation. Some loci of the S genome of Ae. speltoides and the G genome of T. timophevii are closely related, suggesting the same origin of some parts of their genomes. None of the Aegilops genomes analyzed is a close relative of the B genome. The diploid progenitor of the B genome remains unknown.