Effects of Allopolyploidization and Homoeologous Chromosomal Segment Exchange on Homoeolog Expression in a Synthetic Allotetraploid Wheat under Variable Environmental Conditions.

Allopolyploidy through the combination of divergent genomes into a common nucleus at doubled dosage is known as a potent genetic and evolutionary force. As a macromutation, a striking feature of allopolyploidy in comparison with other mutational processes is that 'genome shock' can be evoked, thereby generating rapid and saltational biological consequences. A major manifestation of genome shock is genome-wide gene expression rewiring, which previously remained to be fully elucidated. Here, using a large set of RNAseq-based transcriptomic data of a synthetic allotetraploid wheat (genome AADD) and its parental species, we performed in-depth analyses of changes in the genome-wide gene expression under diverse environmental conditions at the subgenome (homoeolog) level and investigated the additional effects of homoeologous chromosomal segment exchanges (abbreviated HEs). We show that allopolyploidy caused large-scale changes in gene expression that were variable across the conditions and exacerbated by both stresses and HEs. Moreover, although both subgenomes (A and D) showed clear commonality in the changes, they responded differentially under variable conditions. The subgenome- and condition-dependent differentially expressed genes were enriched for different gene ontology terms implicating different biological functions. Our results provide new insights into the direct impacts of allopolyploidy on condition-dependent changes in subgenome expression and the additional effects of HEs in nascent allopolyploidy.