The Solanaceae, Rosaceae, and Scrophulariaceae families all possess an RNase-mediated self-incompatibility mechanism through which their pistils can recognize and reject self-pollen to prevent inbreeding. The highly polymorphic S-locus controls the self-incompatibility interaction, and the S-locus of the Solanaceae has been shown to be a multi-gene complex in excess of 1.3 Mb. To date, the function of only one of the S-locus genes, the S-RNase gene, has been determined. This article reviews the

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... current status of the search for the pollen S-gene and the current models for how S-haplotype speci®c inhibition of pollen tubes can be accomplished by S-RNases.