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Title: Rapid genome evolution as revealed by comparative sequence analysis of orthologous regions from four triticeae genomes

item Gu, Yong
item Coleman-Derr, Devin
item Anderson, Olin

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/3/2004
Publication Date: 4/30/2004
Citation: Gu, Y.Q., Coleman-Derr, D., Kong, X., Anderson, O.D. 2004. Dynamics and rapid genome evolution in allopolyploid wheat as revealed by comparative sequence analysis of the complex hmw-glutenin locus regions. Plant Physiology. 135:459-470.

Interpretive Summary: The unique ability of wheat flour to form doughs is primarily determined by the storage proteins in the wheat seeds. One such storage protein is the high molecular weight (HMW) glutenin. However, bread wheat is hexaploid species, consisting of three different, but highly related genomes, termed A, B, and D. Each genome contributes seven pairs of chromosomes. Genes encoding the HMW-glutenin protein are located in the Chromosome 1 from each genome. Furthermore, the HMW-glutenin genes is duplicate in each genome, thus, there are total of six HMW-glutenin genes in bread wheat. Previous studies demonstrated that these six genes are not always expressed in wheat. To understand the complexity of these genes in different wheat genomes, we isolated and sequenced a large region of B genome containing both HMW-glutenin genes. Sequence analysis revealed that in addition to the two HMW-glutenin genes, other storage protein gene, globulin, was identified adjacent to one of the HMW-glutenin genes. Two protein kinases were identified in the sequenced region. The results provide a detailed review of the chromosome region containing the critical wheat storage protein genes and will help design better biotechnological strategies for the improvement of wheat quality.

Technical Abstract: Bread wheat (Triticum aestivum) is a hexaploid species, consisting of three subgenomes (A, B, and D). To study the molecular evolution of these closely related genomes, we compared the sequence of a 307-kb physical contig covering the HMW-glutenin locus from the A genome of durum wheat Triticum turgidum (AABB) with the orthologous regions from the B genome of the same wheat and the D genome of the diploid wheat Aegilops tauschii (Anderson et al., 2003, Kong et al., 2003). Although gene colinearity appears to be retained, four out of six genes including the two paralogous HMW-glutenin genes were disrupted in the orthologous region of the A genome. Mechanisms involved in gene disruption in the A genome include retroelement insertions, sequence deletions, and mutations causing in-frame stop codons in the coding sequences. Comparative sequence analysis also revealed that sequences in the colinear intergenic regions from these different wheat genomes were generally not conserved. The rapid genome evolution in these regions is mainly attributable to the large number of retrotransposon insertions that occurred after the divergence of the three wheat genomes. Our comparative studies indicate that the B genome diverged prior to the separation of the A and D genomes. Furthermore, sequence comparison of two distinct types of allelic variations at the HMW-glutenin loci in the A genomes of different hexaploid wheat cultivars with the A genome locus of durum wheat indicates that hexaploid wheat may have more than one tetraploid ancestor.