Whether sex chromosomes are differentiated is an important aspect of our knowledge of dioecious plants, such as date palm (Phoenix dactylifera). In this crop plant, the female individuals produce dates, and are thus the more valuable sex. 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 found three genetically linked microsatellite loci that are heterozygous only in males. These results confirm the existence of an XY chromosomal system with a non recombining XY-like region in the date palm genome. The distribution of Y haplotypes in western and eastern haplogroups allowed us to trace two male ancestral paternal lineages that account for all known Y diversity in date palm. The very low diversity associated with Y haplotypes is consistent with clonal paternal transmission of a nonrecombining male-determining region. Our results establish the date palm as a biological model with one of the most ancient sex chromosomes in flowering plants. We have investigated the cessation of recombination in the sex determination region within the genus
Phoenix as a whole by extending the analysis of
P.
dactylifera SSR sex-related loci to eight other species within the genus. Phylogenetic analysis of a date palm sex-linked
PdMYB1 gene in these species has revealed that sex-linked alleles haven’t clustered in a species-dependent way but rather in X and Y allele clusters. Our data show that sex chromosomes evolved from a common autosomal origin before the diversification of the extant dioecious species. Recent results on the investigation of the sex linked loci in other palms are also presented.
Frédérique Aberlenc-Bertossi1, Salwa Zehdi-Azouzi2, Amandine Crabos1, Karina Castillo1, Nathalie Chabrillange1, Jean-Christophe Pintaud3, Amel Salhi-Hannachi2, Sylvain Glémin4,5 and Emira Cherif1,2
1IRD/CIRAD F2F-palm group, UMR DIADE, Centre IRD, 911 avenue Agropolis, 34394, Montpellier, France;
2Laboratoire de Génétique Moléculaire, Immunologie et Biotechnologie, Faculté des sciences de Tunis, Université de Tunis El Manar, Campus Universitaire, 2092, El Manar, Tunisia;
3Dynadiv, UMR DIADE, Centre IRD, 911 avenue Agropolis, 34394, Montpellier, France;
4Institut des Sciences de l’Evolution de Montpellier, Unité Mixte de Recherche 5554 (Université de Montpellier-CNRS-IRD-EPHE), 34095, Montpellier, France
5Department of Ecology and Genetics, Evolutionary Biology Centre, Uppsala University, SE-752 36 Uppsala, Sweden.
Key words: Phoenix dactylifera, sex-linked gene, sex chromosomes, recombination arrest, dioecy, speciation.
