Plant & Animal Genomes XI Conference Plant & Animal Genomes XI ConferenceJanuary 11-15, 2003
Town & Country Convention Center
San Diego, CA
Workshop: Fruit and Nut Crops
Carica papaya is a polygamous plant species with female, male, and hermaphrodite sexes. Sexual polymorphism makes papaya a model plant for studying sex determination and differentiation. Classical genetic analyses led to the conclusion that sex determination in papaya is the result of a single gene with three alleles. We are using three hermaphrodite sex-linked markers, W11, T12 and CPBE55 for fine mapping of the sex locus on 991 F2 and 755 F3 individuals derived from the two cultivars Kapoho and SunUp. No recombination was found among these three markers in either the F2 or F3 populations. BAC end cloning and chromosome walking have allowed construction of a 900 kb BAC DNA contig containing the W11, CPBE55, and T12 markers. The physical distance between W11 and CPBE55, CPBE55 and T12, W11 and T12 is 500 kb, 400 bp and 900 kb, respectively. The large distance spanned suggests severe suppression of recombination in the genomic region that harbors the sex determination gene. We also cloned and sequenced 62 hermaphrodite sex-linked AFLP fragments based on a mapping population of 54 F2 plants. Forty-three SCAR markers were developed and 27 of them were used to screen a papaya BAC library. Six hermaphrodite sex-related BAC contigs have been constructed with genome coverage of 200 to 900 kb each. The overall coverage by all sex related BAC contigs currently extends to more than 2 Mbp. Southern hybridization of three markers on BAC contigs reveal three duplicated segments in this genomic region. Southern hybridization of selected markers to total genomic DNA of the three sex types indicates that these markers are present only in male and hermaphrodite plants but not in female plants. Chromosome in situ hybridization is under way to determine the physical location of the sex determination gene.