1 Non - Additive Expression of Homoeologous Genes is Established Upon Polyploidization in 2 Hexaploid Wheat 3 4 5

44 Effects of polyploidy in allohexaploid wheat (Triticum aestivum L.) have primarily been ascribed 45 to increases in coding sequence variation and potential to acquire new gene functions through 46 mutation of redundant loci. However, regulatory variation that arises through new promoter and 47 transcription factor combinations or epigenetic events may also contribute to the effects of 48 polyploidization. In the present study, gene expression was characterized in a synthetic T. 49 aestivum line and the T. turgidum and Aegilops tauschii parents in order to establish a timeline 50 for such regulatory changes and estimate the frequency of non-additive expression of 51 homoeologous transcripts in newly-formed T. aestivum. Large-scale analysis of non-additive 52 gene expression was assayed by microarray expression experiments, where synthetic T. aestivum 53 gene expression was compared to additive model values (mid-parent) calculated from parental T. 54 turgidum and Ae. tauschii expression levels. Approximately 16% of genes were estimated to 55 display non-additive expression in synthetic T. aestivum. A certain fraction of the genes (2.9%) 56 showed overdominance or underdominance. cDNA-SSCP analysis was applied to measure 57 expression of homoeologous transcripts and further verify microarray data. The results 58 demonstrate that allopolyploidization, per se, results in rapid initiation of differential expression 59 of homoeologous loci and non-additive gene expression in T. aestivum.