Identification of self-incompatibility (S-) locus linked pollen cDNA markers in Petunia inflata

Solanaceous type self-incompatibility (SI) is controlled by a single polymo rphic locus, termed the S-locus. The only gene at the S-locus that has been characterized thus far is the S-RNase gene, which controls pistil function , but not pollen function, in SI interactions between pistil and pollen. On e approach to identifying additional genes (including the pollen S-gene, wh ich controls pollen function in SI) at the S-locus and to study the structu ral organization of the S-locus is chromosome walking from the S-RNase gene . However, the presence of highly repetitive sequences in its flanking regi ons has made this approach difficult so far. Here, we used RNA differential display to identify pollen cDNAs of Petunia inflata, a self-incompatible s olanaceous species, which exhibited restriction fragment length polymorphis m (RFLP) for at least one of the three S-haplotypes (S-1, S-2, and S-3) exa mined. We found that the genes corresponding to 10 groups of pollen cDNAs a re genetically tightly linked to the S-RNase gene. These cDNA markers will expedite the mapping and cloning of the chromosomal region of the Solanacea e S-locus by providing multiple starting points.