Phylogenomics unravels the complex reticulated history and shifts in mating systems in wheat relatives (Aegilops/Triticum genus)

AGAP : Equipe GE2POPInternational audienceEvolution from outcrossing to selfing recurrently occurred in many groups of organisms, especially in plants. Although it could be advantageous on the short term, selfing is though to be a dead-end strategy because (i) selfing is expected to reduce the efficacy of selection and (ii) back transitions towards outcrossing are assumed to be unlikely. Genomic approaches allow both to reconstruct species and mating system histories and to investigate the genomic consequences of mating system transitions. The Aegilops/Triticum genus (wheat relatives) contains both self-incompatible and selfcompatible species with different degree of selfing. For all 13 diploid species of the genus and four outgroups we better characterized their mating systems by a combinations of morphological measures on several reproductive traits. For each species we also sequenced the transcriptome of at least two individuals (up to 10 or 20 individuals for some focal outcrossing and selfing species, respectively). First, we reconstructed the complex history of the genus. We confirmed one recently proposed event of genomic material exchange either through hybridization or intensive gene flow, and we pointed to at least a new, more recent, one. Mapping traits on this historical background reveals that self-incompatibility was ancestral and lost only once, followed by several independent evolution events towards more or less high selfing rates. Across species we found a strong negative association between the level of selfing and both polymorphism levels and selection efficacy. However, we did not find any evidence of relaxed selection efficacy on ancestral lineages leading to the extent selfing species, suggesting that high selfing habit is of recent origin. In addition to support the dead-end hypothesis, these results also provide a time-scale for the dynamics of selfing evolution