This family consists of a series of plant proteins which are related to the Papaver rhoeas S1 self-incompatibility protein. Self incompatibility (SI) is the single most important outbreeding device found in angiosperms and is a mechanism that regulates the acceptance or rejection of pollen. S1 is known to exhibit specific pollen-inhibitory properties [1].

1: Cloning and expression of a distinctive class of self-incompatibility (S) gene from Papaver rhoeas L. Foote HC, Ride JP, Franklin-Tong VE, Walker EA, Lawrence MJ, Franklin FC; Proc Natl Acad Sci U S A 1994;91:2265-2269. PMID:8134385