Submitted to: Plant Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/23/2003
Publication Date: 1/30/2004
Citation: Kong, X., Gu, Y.Q., You, F.M., Dubcovsky, J., Anderson, O.D. 2004. Dynamics of the evolution of orthologous and paralogous portions of a complex locus region in two genomes of allopolyploid wheat. Plant Molecular Biology. 54:55-69. Interpretive Summary: High Molecular Weight (HMW) glutenin is the major determinant of the breadmaking quality of wheat flour. To understand the evolution of this critical protein in wheat, we isolated large DNA fragments carrying the HMW-glutenin gene and its surrounding regions from the B genome of the durum wheat. The large DNA fragments were completely sequenced. The sequence information was analyzed in detail and compared with the D genome HMW-glutenin region. Conserved and divergent sequences were identified in these revolutionary related regions, revealing a dynamic and rapid genome changes occurred in the history of wheat genome evolution. In addition, several genes other than the HMW-glutenin were identified in the surrounding regions of the HMW-glutenin gene. Further analyses of these sequences will enable us to identify sequence elements controlling the expression of these genes in wheat.
Technical Abstract: Two overlapping bacterial artificial chromosome (BAC) clones from the B genome of the tetraploid wheat Triticum turgidum were identified, each of which contains one of the two HMW-glutenin genes, comprising the complex Glu-B1 locus. The complete sequence (285,506 bp of DNA) of this chromosomal region was determined. The two paralogous x- (Glu-1-1) and y- (Glu-1-2) type high-molecular-weight (HMW) glutenin genes of the complex Glu-B1 locus were found to be separated by approximately 168,000 bp instead of the 51,000 bp separation previously reported for the orthologous Glu-D1 locus of Aegilops tauschii, the D-genome donor of hexaploid wheat. This difference in intergene spacing is due almost entirely to be the insertion of clusters of nested retrotransposons. Otherwise, the orientation and order of the HMW-glutenins and adjacent genes was identical in the two genomes. A comparison of these orthologous regions indicates modes and patterns of sequence divergence, with implications for the overall Triticeae genome structure and evolution. A duplicate globulin gene, found 5' of each HMW-glutenin gene, assists to tentatively define the original duplication event leading to the paralogous x- and y-type HMW-glutenin genes. The intergenic regions of the two loci are composed of different patterns and classes of retrotransposons, indicating that insertion times of these retroelements were after the divergence of the two wheat genomes. In addition, a putative receptor kinase gene near the y-type HMW-glutenin gene at the Glu-B1 locus is likely active as it matches recently reported ESTs from germinating barley endosperm. The presence of four genes represented only in the Triticeae endosperm ESTs suggests an endosperm-specific chromosome domain.