The impact of alloploidy on gene expression in Dactylorhiza.
Date:
Talk at International Conference on Polyploidy, Hybridization and Biodiversity, Rovinj, Croatia
Abstract: Recurrent origins are the rule for most polyploids. This can create an array of genetically, ecologically, independent assortment and recombination may produce additional variation. As these multiple origins provide natural replicates, sibling allopolyploids are excellent models to uncover mechanisms of adaptation to divergent environments, which are assumed to lead to evolutionary diversification and biodiversity increase. Our study focuses on three ecologically divergent, sibling allopolyploid orchids of different moderate ages (Dactylorhiza majalis, D. traunsteineri and D. ebudensis). These species have been formed through unidirectional hybridization between diploids D. fuchsii (always the maternal parent) and D. incarnata (always the paternal parent). Given the working hypothesis that in the short evolutionary times relevant to our study system, phenotypic divergence relies on quantitative differential gene expression rather than differences in the coding DNA sequence, we are specifically searching for genes that are differentially expressed between our allopolyploids. To show this, we are using RNA-seq data obtained for 30 individuals representing the three sibling allopolyploids and their diploid parents. Our results suggest that, although morphologically and ecologically divergent, the Alpine and certain Scandinavian D. traunsteineri resemble more D. majalis than the British D. traunsteineri. Furthermore, the gene expression patterns of the Scottish endemic D. ebudensis closely resemble those of the British D. traunsteineri. These results suggest that an ongoing gene flow between sympatric allopolyploids broadly homogenizes their gene expression, whereas their phenotypic divergence is controlled by a restricted set of genes. Indeed, an enrichment for certain ecologically important functional pathways, for example the response to abiotic stress, has been found within the differentially expressed genes between D. traunsteineri and D. majalis. In addition, the results of a recently developed method (HyLiTE) point to homoeolog expression bias, expression level dominance and the possible link of these effects on the divergent adaptation of our naturally occurring allopolyploid species.