, Volume 20, Issue 2, pp 63-72
Date: 06 Mar 2007

Physical size of the S locus region defined by genetic recombination and genome sequencing in Ipomoea trifida, Convolvulaceae

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Sporophytic self-incompatibility (SSI) in the genus Ipomoea (Convolvulaceae) is controlled by a single polymorphic S locus. We have previously analyzed genomic sequences of an approximately 300 kb region spanning the S locus of the S 1 haplotype and characterized the genomic structure around this locus. Here, we further define the physical size of the S locus region by mapping recombination breakpoints, based on sequence analysis of PCR fragments amplified from the genomic DNA of recombinants. From the recombination analysis, the S locus of the S 1 haplotype was delimited to a 0.23 cM region of the linkage map, which corresponds to a maximum physical size of 212 kb. To analyze differences in genomic organization between S haplotypes, fosmid contigs spanning approximately 67 kb of the S 10 haplotype were sequenced. Comparison with the S 1 genomic sequence revealed that the S haplotype-specific divergent regions (SDRs) spanned 50.7 and 34.5 kb in the S 1 and S 10 haplotypes, respectively and that their flanking regions showed a high sequence similarity. In the sequenced region of the S 10 haplotype, five of the 12 predicted open reading frames (ORFs) were found to be located in the divergent region and showed co-linear organization of genes between the two S haplotypes. Based on the size of the SDRs, the physical size of the S locus was estimated to fall within the range 34–50 kb in Ipomoea.
Communicated by Noni Franklin-Tong.