Characterization of the S-locus region of almond (Prunus dulcis): Analysisof a somaclonal mutant and a cosmid contig for an S haplotype

Almond has re self-incompatibility system that is controlled by an S locus consisting of the S-RNase gene and an unidentified "pollen S gene." An almo nd cultivar "Jeffries," a somaclonal mutant of "Nonpareil" ((SSd)-S-c), has a dysfunctional S-c haplotype both in pistil and pollen. Immunoblot and ge nomic Southern blot analyses detected no S-c haplotype-specific signal in J effries. Southern blot showed that Jeffries has an extra copy of tile S-d h aplotype. These results indicate that at least two mutations had occurred t o generate Jeffries: (1) deletion of the S-c haplotype and (2) duplication of the S-d haplotype. To analyze the extent of the deletion in Jeffries and gain insight into the physical limit of the S locus region, similar to 200 kbp of a cosmid contig for the S-c haplotype was constructed. Genomic Sout hern blot analyses showed that tile deletion in Jeffries extends beyond the region covered by the contig. Most cosmid end probes, except those near th e S-c-RNase gene, ecross-hybridized with DNA fragments from different S hap lotypes. This suggests that regions away from the S-c-RNase gene call recom bine between different S haplotypes, implying that the cosmid contig extend s to the borders of the S locus.