|Bai, Jianfa - KANSAS STATE UNIVERSITY|
|L Chingcuanco, Debbie|
|Gill, Bikram - KANSAS STATE UNIVERSITY|
Submitted to: Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 15, 2008
Publication Date: March 1, 2009
Citation: Pumphrey, M.O., Bai, J., Chingcuanco, D.L., Anderson, O.D., Gill, B. 2009. Non-Additive Expression of Homoeologous Genes is Established Upon Polyploidization in Hexaploid Wheat. Genetics. 181(3):1147-1157. Interpretive Summary: The wheat family contains species that are diploid (2 copies of each gene), tetraploid (four copies of each gene), and hexaploid (six copies of each gene). Hexaploid bread wheat is thought to originate from a natural cross that occurred thousands of years ago between diploid and tetraploid wheat relatives. An interesting question in the evolution of hexaploid bread wheat is how the multiple copies of genes interact with each other and possibly adapt over time to optimize growth of the hexaploid plant. Gene expression level was measured for thousands of genes in a diploid wheat (goatgrass), a tetraploid wheat (durum), and a new hexaploid wheat that was derived by crossing the diploid and the tetraploid. About 16% of the genes were altered in expression in the new hexaploid compared to the wild relatives. These results may help identify gene interactions that are important in hexaploid bread wheat.
Technical Abstract: Traditional views on the potential genetic effects of polyploidy in allohexaploid wheat (Triticum aestivum L.) have primarily emphasized aspects of greater coding sequence variation and the enhanced potential to acquire new gene functions through mutation of redundant loci. The extent and significance of regulatory variation has been relatively unexplored. Recent investigations suggest that differential expression of homoeologous transcripts is common in wheat. In order to establish a timeline for such regulatory changes and estimate the frequency of non-additive expression of homoeologous transcripts in newly-formed T. aestivum, gene expression was characterized in a synthetic T. aestivum line and T. turgidum and Aegilops tauschii parents. Applying cDNA-SSCP analysis to study 30 arbitrarily-selected homoeologous transcripts revealed that four (~13%) showed differential expression of homoeoalleles in seedling leaf tissue of synthetic T. aestivum. In microarray expression experiments, synthetic T. aestivum gene expression was compared to mid-parent expression model values calculated from parental T. turgidum and Ae. tauschii expression levels. Approximately 16% of genes were estimated to display non-additive expression in synthetic T. aestivum. Homoeolog expression patterns of non-additive transcripts identified by microarrays suggest that cis-acting regulatory variation is often responsible for non-additive gene expression levels. These results demonstrate that allopolyploidization, per se, results in rapid initiation of differential expression of homoeologous loci and non-additive gene expression in T. aestivum.