XVI International Botanical Congess

SI in Papaver rhoeas is controlled by a single, multi-allelic, gametophytically expressed S locus. We have cloned genes encoding stigmatic and pollen components that mediate this cellular recognition system and explored their interaction using site-directed mutagenesis. Although the stigmatic S genes do not exhibit homology to known S genes from other species, we have identified a novel gene family in Arabidopsis of S protein homologues. Preliminary studies indicate that these expressed. S allele specific interaction between stigmatic S proteins and a pollen receptor results in the activation of a calcium dependent signal transduction pathway and present evidence that it ultimately activates a programmed cell-death pathway in the incompatible pollen.