Self-incompatibility in Papaver targets soluble inorganic pyrophosphatases in pollen

Self-incompatibility is an important tactic used by higher plants to avoid self fertilization, thereby ensuring the production of new genotypes. In the corn poppy Papaver rhoeas, the self-incompatibility response triggers a Ca2+-dependent signalling network, resulting in the rapid arrest of 'self' pollen tube growth. The pollen protein p26 is one of the earliest targets for self-incompatibility signals. Now de Graaf et al. show that p26 is made up of two soluble inorganic pyrophosphatases (sPPases). PPases are highly conserved across prokaryotes and eukaryotes; via hydrolysis of inorganic pyrophosphate, they provide the driving force for many metabolic reactions. This work marks out PPases as important regulators of pollen growth, and also identifies a previously unreported regulatory mechanism for the inhibition of this important class of enzymes.