Gene-specific sex-linked genetic markers in date palm (Phoenix dactylifera L.)

During the past decade, there have been numerous attempts to identify sex-linked molecular genetic markers that can be used to discriminate among male and female trees in date palm (Phoenix dactylifera L.). In our approach to address this biological problem, we applied a comparative genomics approach and used a candidate sex-linked Tormozembryo Defective (TOZ19) gene found to be male-specific in aspen. Using BLAST against the date palm genome assembly, we found a putative Transducin Beta-like Protein 3 (TBL3) gene in date palm that was highly homologous to the TOZ19 gene and sequenced it in three male and four female trees from four economically important date palm cultivars from Egypt. Based on the obtained multiple nucleotide sequence alignments, male- and female-specific date palm haplotypes were identified by screening single nucleotide polymorphisms (SNPs). Subsequently, a respective gene fragment in additional five date palm samples comprising three females and two males were cloned and sequenced to independently confirm the previously identified putative sex-linked SNPs. The three putative sex-linked SNPs can be used now to discriminate male and female date palms at their seedling stage. This will further enhance and pave the way for commercial date palm cultivation through seeds. The identified molecular markers are relatively easy, cheap, fast, and reproducible sex identification tools. Female date palms are either homozygous or heterozygous, while male date palms are hemizygous at the putative sex-linked loci.