Positional cloning of the s haplotype determining the floral and incompatibility phenotype of the long-styled morph of distylous Turnera subulata.
Heterostyly is a plant breeding system occurring in approximately 28 plant families and it has often been used as a model system in plant genetics and evolution. Although heterostyly has been studied for over a century beginning with Charles Darwin, the genes determining floral architecture and incompatibility are still unknown. To identify the genes residing at the S-locus of distylous Turnera subulata, we used a positional cloning strategy and assembled three BAC contigs across the S-locus region. In total, 31 overlapping BAC clones were assembled into contigs 1, 2 and SL. We developed and mapped numerous co-dominant markers from the ends of BAC clones across the S-locus region and assayed X-ray deletion mutants to delimit the region of the contig containing the S-locus. Deletion mapping revealed that a single BAC clone (L22s) within contig-SL contains the s haplotype, while two additional BAC clones (I1 and K15) may contain parts of the dominant S haplotype. Furthermore, we exploited the contigs assembled and investigated the rates of recombination at the S-locus as well as in two regions on either side of the S-locus. We found that recombination rates (estimated in kb/cM) are 2-5 times lower at the S-locus relative to flanking regions, although they are not statistically significant. The present study represents a landmark in the molecular characterization of the S-locus of a heterostylous species. We are now on the verge of identifying the genes that have remained elusive since Darwin's comprehensive study of heterostylous systems more than 125 years ago.
Department of Biology, York University, 4700 Keele Street, Toronto, ON M3J 1P3, Canada.
Jonathan D J
JD
Labonne
Joel S
JS
Shore
D003001:Cloning, Molecular; D035264:Flowers / Q000235:genetics* / Q000502:physiology; D006239:Haplotypes; D009154:Mutation; D010641:Phenotype; D029647:Turnera / Q000235:genetics* / Q000502:physiology