Gene Expression Changes In Early Stages Of Allohexaploid Wheat Formation

Common wheat(Triticum aestivum L., 2n=6x=42, BBAADD) is a grain originated in the fertile Crescent of the Middle East region, now widely distributed all over the world. Common wheat experienced two allopolyploidization events in its evolution history, and it is a classic case of one step formation of a new species. Allopolyploidization unit two or more genomes from different species into one nucleus and will cause a lot of dramatic changes. The combined genomes in allopolyploidy will undergo "genome shock", which include structural rearrangements, transposon activation, epigenetic modifications and changes in gene expression.To explore the transcriptomic dynamics accompanying early stages of allopolyploidy formation, we utilize two synthetic allohexaploid wheat lines as materials which have the same parent composition. Using GISH, we found that in addition to the presence of individual plant such as aneuploidy, chromosomal translocation, the newly synthesized allohexaploid wheat genome is relatively stable in general. Genome-wide analysis of gene expression was performed for those two alloheaxploid lines and their parents, using Affymetrix Gene Chip wheat Genome Array. Transcriptomic divergence between parents was 47.99%, the transcriptomic divergence between synthesized allohexaploid and diploid parent is greater than that of between the synthesized allohexaploid and tetraploid parent. This result is consistent with the two-third and one-third genomic contributions by the tetraploid and diploid parent, respectively. In these two synthetic allohexaploid lines we all detected parental dominance expression, but although the number of parental dominance expression genes was generally the same, but they overlap little with each other. In newly synthesized allohexaploid wheat most of genes exhibited additive expression, and only a small part of the gene showed non-additive expression. Only a small part of non-additive gene expression showed transgressive expression. The non-additive genes could be classified into four distinct groups: common between the two lines and heritable, heritable, stochastic and always change. No GO functional enrichment was found among those non-additive gene which were common between the two lines and heritable. The stochastic non-additive genes were involved in various GO terms. After high temperature and salt treatment, the phenotype of synthetic allohexaploid wheat changed, and these phenotype changes differ between the two synthetic lines and each selfed generations.