In Solanaceae-type self-incompatibility, the specificity of self/non-self interactions between pollen and pistil is controlled by two polymorphic genes at the S-locus, with S-locus F-box gene (SLF or SFB) controlling pollen specificity and S-RNase gene controlling pistil specificity. Meng et al. summarize their recent results on the identification and functional studies of S-RNase and SLF in Petunia inflata, and a protein-degradation model is proposed to explain the biochemical mechanism for specific rejection of self-pollen tubes by the pistil.