A Very Ancient XY Chromosome System In Plant Revealed By Sex-Linked Molecular Markers In Date Palm

Dioecy in plants is the equivalent of gonochory in animals, i.e. a rigorous separation of the sexes. Differentiation of sex chromosomes is an important aspect of our knowledge of dioecious plants, notably for date palm.  In this crop plant, only females are valuable since they produce dates. However, there is no way to identify the sex of date palm plants before reproductive age, and the sex-determining mechanism is still unclear. We thus conducted a large-scale population genetics survey, using simple sequence repeat (SSR) markers and identified three reliable sex-linked loci producing male specific alleles allowing us to identify the gender in 100% individuals. These results confirmed the existence of an XY chromosomal system with a non-recombining XY-like region in the date palm genome. Furthermore a very low diversity associated with Y haplotypes is generated by these loci, which is consistent with a clonal paternal transmission of a non-recombining male-determining region. These results have established the date palm as a biological model with one of the most ancient sex chromosomes in flowering plants.