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Title: Rapid evolution and complex structural organization in genomic regions harboring multiple prolamin genes in the polyploid wheat genome

item Gu, Yong
item Anderson, Olin

Submitted to: Plant Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/2/2007
Publication Date: 7/16/2007
Citation: Gao, S., Gu, Y.Q., Wu, J., Huo, N., Crossman, C., Jia, J., Ren, Z., Anderson, O.D., Xiuying, K. 2007. Rapid evolution and complex structural organization in genomic regions harboring multiple prolamin genes in the polyploid wheat genome. Plant Molecular Biology. 65:189-203.

Interpretive Summary: Prolamins, rich in praline and glutamine, are major seed storage proteins in the endosperm of wheat grains. Wheat prolamins can be divided into two major groups, glutenins and gliadins. The bread-making quality of wheat flour is largely determined by the complex relations of different prolamin components in the endosperm. In this study, we studied genetic loci containing multiple wheat prolamin genes. Our result revealed the complexity of genomic regions harboring wheat prolamin genes. However, this work also provided important knowledge on the evolution of wheat genomes and could help us design effective strategies to tackle the wheat’s large and complex genome for crop improvement.

Technical Abstract: Genes encoding wheat prolamins belong to complicated multi-gene families in the wheat genome. To understand the structural complexity of storage protein loci, we sequenced and analyzed orthologous regions containing both gliadin and LMW-glutenin genes from the A and B genomes of a tetraploid wheat species, Triticum turgidum ssp. durum. Despite their physical proximity to one another, the gliadin genes and LMW-glutenin genes are organized quite differently. The gliadin genes are found to be more clustered than the LMW-glutenin genes which are separated from each other by much larger distances. The separation of the LMW-glutenin genes is the result of both the insertion of large blocks of repetitive DNA owing to the rapid amplification of retrotransposons and the presence of genetic loci interspersed between them. Sequence comparisons of the orthologous regions reveal that gene movement could be one of the major factors contributing to the violation of microcolinearity between the homoeologous A and B genomes in wheat. The rapid sequence rearrangements and differential insertion of repetitive DNA has caused the gene islands to be not conserved in compared regions. In addition, we demonstrated that the i-type LMW-glutenin originated from a deletion of 33-bps in the 5’ coding region of the m-type gene. Our results show that multiple rounds of segmental duplication of prolamin genes have driven the amplification of the -gliadin genes in the region; such segmental duplication could greatly increases the repetitive DNA content in the genome depending on the amount of repetitive DNA present in the original duplicate region.