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Consequences of polyploidy events on angiosperm genome evolution
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Edité par CCSD -
International audience. In plants, polyploidy is a widespread phenomenon with major consequences on genome evolution. It is considered as a major process of speciation, diversification and ecological adaptation of plants. Polyploidy is the inherited condition of having more than two complete sets of chromosomes resulting from whole genome duplication. Polyploidization is quite common in the plant kingdom. About half of current flowering plants are polyploids.The aim of this study is to understand the polyploidy impact on evolution and conservation of flowering plants by comparing the genomes of 84 angiosperm species. Does polyploidization drive sequence diversity? Can we determine divergence time and the age of polyploidization events from sequence diversity?Here, using comparative genomics, we identified 81,700 conserved gene families between the 84 species (including 61% with at least two species). Since these species have gone through at least one round of duplication, it is assumed that they should have few or no conserved single-copy genes. However, 3,249 gene families containing at least 50 species with singleton genes were identified. The number of single copy genes varies widely between species. Indeed, after a polyploidization event, there is a gradual loss of duplicated genes, as the genome tends to return to a diploid state. Thus, single copy genes were used as an index to categorize recent or ancient polyploids. Similarly, the analysis of GC content and amino acid composition showed that the sequence profiles in monocots and eudicots are different while polyploidy does not impact sequence diversity. Finally, using synonymous substitution (Ks) rates, we were able to estimate divergence time (speciation) and infer the age of polyploidy events over nearly 250 million years of angiosperm evolution.
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