S RNASES AND SELF AND NON-SELF POLLEN RECOGNITION IN FLOWERING PLANTS
Self-incompatibility (SI) is an important intraspecific reproductive barrier to prevent self-fertilization in flowering plants. In many cases, SI is controlled by a single multi-allelic locus, the S locus. Molecular analysis of self-incompatible species of the Solanaceae, Scrophulariaceae and Rosaceae have shown that a class of ribonucleases encoded by the S locus, known as S RNases, determine the stylar expression of SI but not its pollen expression. A different gene is thought to control pollen expression of SI (pollen S gene). Here, we present some progress made towards molecular cloning of the pollen S in Antirrhinum using two approaches, S-locus directed transposon tagging and map-based cloning. Possible pathways of how S RNases interact with pollen S gene product to achieve self and non-self pollen recognition are discussed.
