THE S-LOCUS OF FLOWERING PLANTS - WHEN SELF-REJECTION IS SELF-INTEREST

In certain families of flowering plants, a self-incompatibility (SI) locus prevents self-fertilization, by a specific interaction between the S-gene product produced in the pistil and the S-gene products borne on or expressed by the male gametophyte, the pollen grain. The female S-locus gene products for two families showing different types of SI have been putatively identified as major pistil glycoproteins (the S-locus-specific glycoproteins of the Brassicaceae and the S-RNases of the Solanaceae). However, they are distinct in sequence and mode of action. The nature of the S-locus gene product borne by the pollen is still uncertain in both systems.