Papaver rhoeas S-Determinants and the Signaling Networks They Trigger

Abstract

Higher plants use specifi c interactions between pollen and pistil to achieve pollination. Self-incompatibility (SI) is an important mechanism used by many species to prevent inbreeding. It is controlled by a multi-allelic S locus. "Self" (incompatible) pollen is discriminated from "non-self" (compatible) pollen by interaction of pollen and pistil S locus components and is subsequently inhibited. Our studies of the SI system in Papaver rhoeas have revealed that the pistil S locus protein, PrsS, is a small novel secreted protein that interacts with the pollen S locus protein, PrpS, which is a small novel transmembrane protein. This interaction of PrsS with incompatible pollen induces a SI response, involving a Ca 2+ -dependent signaling network, resulting in pollen inhibition and programmed cell death; this provides a neat way to destroy "self"-pollen. Several SI-induced events have been identifi ed, including Ca 2+ and K + infl ux, increases in cytosolic free Ca 2+ , activation of a MAP kinase, alterations to the cytoskeleton, and phosphorylation of a soluble inorganic pyrophosphatase. Here we present an overview of our knowledge of the novel cell-cell recognition S -determinants and the signals, targets, and mechanisms triggered by an incompatible interaction. We hope this review is of interest to those involved in the origins and evolution of cell-cell recognition systems involved in discrimination between "self" and "non-self," which include histocompatibility systems in primitive chordates and vertebrates as well as plant self-incompatibility.