The molecular genetics of self-incompatibility in Petunia hybrida

The cultivated petunia (Petunia hybrida) has been a popular system in which to study genetic, physiological and biochemical aspects of gametophytic se lf-incompatibility. As with other members of the Solanaceae a number of S-R Nase genes have been isolated for functional S-alleles. We have identified S-RNase sequences for two additional functional S-alleles, S-v and S-3. The se alleles are more similar to alleles from other families of the Solanacea e (Nicotiana and Solanum) than to any petunia alleles reported previously. The total number of S-alleles in P. hybrida is at least ten in spite of its cultivated origin. However, most cultivars of P. hybrida are in fact self- compatible and this appears to arise from the prominence of a single previo usly described allele S-o. The implications of this observation for the ori gin of self compatibility in P. hybrida are discussed. The S-locus of P, in br ida has recently been mapped using an indirect method involving T-DNA i nsertions. Seven T-DNA insertions that were previously shown to be closely linked to the S-locus were physically mapped on the long arm of chromosome III using fluorescent in-situ hybridization. The most tightly linked T-DNA insertions are in a sub-centromeric position. This is consistent with the c entric fragments of P. inflata obtained by irradiation mutagenesis that car ry additional S-loci and confer a pollen-part mutant phenotype. An S-linked restriction fragment length polymorphism (RFLP) marker, CP100 was used to confirm this chromosomal assignment and has provided evidence for S-locus s ynteny in the Solanaceae. (C) 2000 Annals of Botany Company.