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Self-incompatibility in Papaver targets soluble inorganic pyrophosphatases in pollen

Naturevolume 444pages490493 (2006) | Download Citation



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’) pollen1. In Papaver rhoeas, S proteins encoded by the stigma interact with incompatible pollen, triggering a Ca2+-dependent signalling network2,3,4,5 resulting in pollen tube inhibition and programmed cell death6. The cytosolic phosphoprotein p26.1, which has been identified in incompatible pollen, shows rapid, self-incompatibility-induced Ca2+-dependent hyperphosphorylation in vivo3. 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.

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We thank G. Wullems for the ntp303 pollen promoter; G. Jones for help and advice on statistical analysis; and E. Sanchez-Moran for help with imaging. Work in the laboratories of F.C.H.F. and V.E.F-T. is funded by the UK Biotechnology and Biological Sciences Research Council. Author Information Sequences have been deposited in the EMBL Nucleotide Sequence Database (http://www.ebi.ac.uk/embl/) under accession codes AM162550 and AM162551. The authors declare no competing financial interests.

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Author notes

    • Jason J. Rudd

    Present address: Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, UK

    • Michael J. Wheeler

    Present address: Institute of Cancer Studies, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK

  1. Barend H. J. de Graaf, Jason J. Rudd and Michael J. Wheeler: These authors contributed equally to this work.


  1. School of Biosciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK

    • Barend H. J. de Graaf
    • , Jason J. Rudd
    • , Michael J. Wheeler
    • , Ruth M. Perry
    • , Elizabeth M. Bell
    • , Kim Osman
    • , F. Christopher H. Franklin
    •  & Vernonica E. Franklin-Tong


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Corresponding author

Correspondence to Vernonica E. Franklin-Tong.

Supplementary information

  1. Supplementary Figure Legends

    This file contains text to accompany Supplementary Figures 1–4. (DOC 32 kb)

  2. Supplementary Figure 1

    Model for sPPase phosphorylation, effect on activity and biological consequences. (PDF 63 kb)

  3. Supplementary Figure 2

    Deduced amino acid sequences of the Pr-p26.1a/b cDNAs. (PDF 138 kb)

  4. Supplementary Figure 3

    sPPase activities in different tissues from Papaver rhoeas (PDF 66 kb)

  5. Supplementary Figure 4

    Antisense oligonucleotides show that Pr-p26.1a/b play a key role in pollen tube growth (PDF 144 kb)

  6. Supplementary Methods

    This file contains additional details on the methods used in this study. (DOC 51 kb)

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