Non-Additive Expression of Homoeologous Genes is Established Upon Polyploidization in Hexaploid Wheat

Effects of polyploidy in allohexaploid wheat (Triticum aestivum L.) have primarily been ascribed to increases in coding sequence variation and potential to acquire new gene functions through mutation of redundant loci. However, regulatory variation that arises through new promoter and transcription factor combinations or epigenetic events may also contribute to the effects of polyploidization. In the present study, gene expression was characterized in a synthetic T. aestivum line and the T. turgidum and Aegilops tauschii parents 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. Large-scale analysis of non-additive gene expression was assayed by microarray expression experiments, where synthetic T. aestivum gene expression was compared to additive model values (mid-parent) 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. A certain fraction of the genes (2.9%) showed overdominance or underdominance. cDNA-SSCP analysis was applied to measure expression of homoeologous transcripts and further verify microarray data. The results demonstrate that allopolyploidization, per se, results in rapid initiation of differential expression of homoeologous loci and non-additive gene expression in T. aestivum.

Key Words: allopolyploid, homoeologous, polyploidy, silencing, wheat

Online ISSN: 1943-2361  Print ISSN: 0016-6731
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