The Papaver Self-Incompatibility Pollen S-Determinant, PrpS, Functions in Arabidopsis thaliana

Summary Many angiosperms use specific interactions between pollen and pistil proteins as "self" recognition and/or rejection mechanisms to prevent self-fertilization. Self-incompatibility (SI) is encoded by a multiallelic S locus, comprising pollen and pistil S -determinants [1, 2]. In Papaver rhoeas , cognate pistil and pollen S -determinants, PrpS, a pollen-expressed transmembrane protein, and PrsS, a pistil-expressed secreted protein [3, 4], interact to trigger a Ca 2+ -dependent signaling network [5–10], resulting in inhibition of pollen tube growth, cytoskeletal alterations [11–13], and programmed cell death (PCD) [14, 15] in incompatible pollen. We introduced the PrpS gene into Arabidopsis thaliana , a self-compatible model plant. Exposing transgenic A. thaliana pollen to recombinant Papaver PrsS protein triggered remarkably similar responses to those observed in incompatible Papaver pollen: S -specific inhibition and hallmark features of Papaver SI [11–15]. Our findings demonstrate that Papaver PrpS is functional in a species with no SI system that diverged ∼140 million years ago [16]. This suggests that the Papaver SI system uses cellular targets that are, perhaps, common to all eudicots and that endogenous signaling components can be recruited to elicit a response that most likely never operated in this species. This will be of interest to biologists interested in the evolution of signaling networks in higher plants.