title: Self-incompatibility in Papaver targets soluble inorganic pyrophosphatases in pollen.
abstract: In higher plants, sexual reproduction involves interactions between pollen and pistil. A key mechanism to prevent inbreeding is self-incompatibility through rejection of incompatible ('self') pollen. In Papaver rhoeas, S proteins encoded by the stigma interact with incompatible pollen, triggering a Ca2+-dependent signalling network resulting in pollen tube inhibition and programmed cell death. The cytosolic phosphoprotein p26.1, which has been identified in incompatible pollen, shows rapid, self-incompatibility-induced Ca2+-dependent hyperphosphorylation in vivo. Here we show that p26.1 comprises two proteins, Pr-p26.1a and Pr-p26.1b, which are soluble inorganic pyrophosphatases (sPPases). These proteins have classic Mg2+-dependent sPPase activity, which is inhibited by Ca2+, and unexpectedly can be phosphorylated in vitro. We show that phosphorylation inhibits sPPase activity, establishing a previously unknown mechanism for regulating eukaryotic sPPases. Reduced sPPase activity is predicted to result in the inhibition of many biosynthetic pathways, suggesting that there may be additional mechanisms of self-incompatibility-mediated pollen tube inhibition. We provide evidence that sPPases are required for growth and that self-incompatibility results in an increase in inorganic pyrophosphate, implying a functional role for Pr-p26.1.
authors.affiliation: School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
authors.forename: Barend H J
authors.initials: BH
authors.lastname: de Graaf
authors.forename: Jason J
authors.initials: JJ
authors.lastname: Rudd
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Wheeler
authors.forename: Ruth M
authors.initials: RM
authors.lastname: Perry
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Bell
authors.forename: Kim
authors.initials: K
authors.lastname: Osman
authors.forename: F Christopher H
authors.initials: FC
authors.lastname: Franklin
authors.forename: Vernonica E
authors.initials: VE
authors.lastname: Franklin-Tong
mesh_terms: D007178:Inbreeding; D008969:Molecular Sequence Data; D010207:Papaver / Q000201:enzymology* / Q000502:physiology; D010750:Phosphoproteins / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism*; D011058:Pollen / Q000201:enzymology*; D053205:Pollen Tube / Q000254:growth & development*; D011755:Pyrophosphatases / Q000737:chemistry / Q000378:metabolism*; D012995:Solubility
chemical_list: D010750:Phosphoproteins; D010940:Plant Proteins; D011755:Pyrophosphatases