SELF-INCOMPATIBILITY IN NICOTIANA-ALATA INVOLVES DEGRADATION OF POLLEN RIBOSOMAL-RNA

GAMETOPHYTIC self-incompatibility is a genetically based system of cellular recognition in plants1. It prevents fertilization by pollen bearing an S-allele identical to either of the two S-alleles present in the female sporophytic tissues. Self-incompatibility in the Solanaceae has been especially well studied and several S-allele specific style glycoproteins identified2-6. In addition, complementary DNAs for nine style S-glycoproteins have been sequenced7-10 and have homology with two fungal ribonucleases. Recently five Nicotiana alata S-glycoproteins were shown to be RNases (S-RNases)11. We now report that S-allele specific degradation of pollen RNA occurs in vivo. After incompatible, but not after compatible pollinations, pollen RNA becomes degraded. This specificity cannot be demonstrated in vitro using isolated S-RNases and pollen RNAs. Our results support a model in which the gametophytic self-incompatibility system in N. alata acts through a cytotoxic mechanism directed against pollen RNA. © 1990 Nature Publishing Group.