Convergent evolution of sex chromosomes in two palm species,Phoenix dactylifera and Kerriodoxa elegans.

Abstract

- In palms, many dioecious species have emerged from at least 8 independent events, yet the mechanisms of sex determination remain poorly understood. Here, we identify and compare the sex chromosomes of Kerriodoxa elegans with those of the well-studied date palm (Phoenix dactylifera), which evolved dioecy independently from a hermaphroditic common ancestor. - We developed target sequence capture kits and inferred sex-linked genes using a probabilistic approach in both species. - We find a striking similarity between the sex-linked regions of K. elegans and P. dactylifera, with the majority of sex-linked genes being common between the two species. However, we confirm that these regions evolved independently, much later than the split between the lineages. - This case of convergent evolution seems to be unique in plants so far, and raises questions on the mechanisms of sex determination. A possible explanation is that this region contains genes related to flower sexual development, and is syntenic in monoecious palm species as well, suggesting it might serve as a genetic toolbox for flower unisexualization in palms.