Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Final Activity and Management Report Summary - DACTGENE (Genetic and epigenetic consequences of hybridization and polyploidy in Dactylorhiza (Orchidaceae))

Hybridisation and polyploidy (the presence of more than two chromosome set in the same nucleus) are known to be major evolutionary forces that have occurred multiple times during the evolution of flowering plants, most probably starting with their origin. Both phenomena have shaped the genome of many crops. The interactions of the conjoined genomes in allopolyploids (organisms combining in each cell nucleus the complete genetic inventory of two other species) induce extensive changes in genomic organisation and gene expression. These alterations stabilise in time the allopolyploid genome; additionally, they may have important phenotypic outcomes (including ecological shifts) and appear as key determinants of the adaptive success of the new allopolyploid species.

The aim of the present project was to uncover the genetic mechanisms of adaptation to divergent environments in independently formed sister allopolyploid orchid taxa. Dactylorhiza majalis, D. traunsteineri and D. ebudensis are all having 80 chromosomes, twice as much as their parents: D. fuchsii and D. incarnata. However, these three allopolyploids differ morphologically and prefer different habitats. By using advanced genomic techniques, our results show that there is a significantly increased range of gene expression in allopolyploids, demonstrating a higher adaptive potential of the allopolyploid group as compared to either parent. There is also strong evidence for an increase in biological complexity in hybrids because they express significantly more genes (including a few novel ones) than the parents at a given point in time. This indicates that in many cases both parental variants of a gene were kept functional. Few gene types do not seem to have been inherited from either parent, but they have rather formed after the allopolyploidisation event, as a result of mutation or recombination.

The novel expressed patterns are the result of modifications of the primary DNA sequence, but also appear after addition or removal of simple chemical marks adjoined to the DNA itself (epigenetic factors), switching on or off the respective gene(s). Several of the investigated genes and epigenetic marks are correlated with environmental parameters (especially temperature and water availability) and/or encode for proteins involved in specific functions of ecological relevance. Multiple origins of each allopolyploid contribute to differential patterns of gene expression with a geographic structure.

However, many patterns are conserved within each allopolyploid but are variable between taxa, indicating that habitat preference shapes similar expression patterns in independently formed allopolyploids. In conclusion, we have demonstrated that in iterative allopolyploidisation evolution doesn't repeat itself, but it can result in quite distinct products with the help of genetic and epigenetic alterations, especially after selection in divergent environments. As our results document divergent ecological adaptation through epigenetic effects, they urge a need to complement our current evolutionary perspective to include the epigenetic level of natural variation when trying to understand population processes that result in adaptation.

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United Kingdom
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