Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Self-incompatibility in Papaver targets soluble inorganic pyrophosphatases in pollen


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.

Your institute does not have access to this article

Relevant articles

Open Access articles citing this article.

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Expression analysis of Pr-p26.1a and Pr-p26.1b sPPases.
Figure 2: Pr-p26.1a and Pr-p26.1b show sPPase activity and are phosphorylated, and phosphorylation affects sPPase activity.
Figure 3: Functional evidence for Pr-p26.1 and sPPase involvement in modulating pollen tube growth.


  1. McClure, B. A. & Franklin-Tong, V. E. Gametophytic self-incompatibility: understanding the cellular mechanisms involved in ‘self’ pollen tube inhibition. Planta 224, 233–245 (2006)

    CAS  Article  Google Scholar 

  2. Franklin-Tong, V. E., Ride, J. P., Read, N. D., Trewavas, A. J. & Franklin, F. C. H. The self-incompatibility response in Papaver rhoeas is mediated by cytosolic-free calcium. Plant J. 4, 163–177 (1993)

    CAS  Article  Google Scholar 

  3. Rudd, J. J., Franklin, F. C. H., Lord, J. M. & Franklin-Tong, V. E. Increased phosphorylation of a 26-kD pollen protein is induced by the self-incompatibility response in Papaver rhoeas.. Plant Cell 8, 713–724 (1996)

    CAS  Article  Google Scholar 

  4. Geitmann, A., Snowman, B. N., Emons, A. M. C. & Franklin-Tong, V. E. Alterations in the actin cytoskeleton of pollen tubes are induced by the self-incompatibility reaction in Papaver rhoeas.. Plant Cell 12, 1239–1251 (2000)

    CAS  Article  Google Scholar 

  5. Snowman, B. N., Kovar, D. R., Shevchenko, G., Franklin-Tong, V. E. & Staiger, C. J. Signal-mediated depolymerization of actin in pollen during the self-incompatibility response. Plant Cell 14, 2613–2626 (2002)

    CAS  Article  Google Scholar 

  6. Thomas, S. G. & Franklin-Tong, V. E. Self-incompatibility triggers programmed cell death in Papaver pollen. Nature 429, 305–309 (2004)

    ADS  CAS  Article  Google Scholar 

  7. Kornberg, A. On the Metabolic Significance of Phosphorolytic and Pyrophosphorolytic Reactions (eds Kasha, H. & Pullman, P.) (Academic Press, New York, 1962)

    Google Scholar 

  8. Cooperman, B. S., Baykov, A. A. & Lahti, R. Evolutionary conservation of the active site of soluble inorganic pyrophosphatase. Trends Biochem. Sci. 17, 262–266 (1992)

    CAS  Article  Google Scholar 

  9. Sivula, T. et al. Evolutionary aspects of inorganic pyrophosphatase. FEBS Lett. 454, 75–80 (1999)

    CAS  Article  Google Scholar 

  10. du Jardin, P., Rojas-Beltran, J., Gebhardt, C. & Brasseur, R. Molecular cloning and characterization of a soluble inorganic pyrophosphatase in potato. Plant Physiol. 109, 853–860 (1995)

    CAS  Article  Google Scholar 

  11. Visser, K., Heimovaara-Dijkstra, S., Kijne, J. W. & Wang, M. Molecular cloning and characterization of an inorganic pyrophosphatase from barley. Plant Mol. Biol. 37, 131–140 (1998)

    CAS  Article  Google Scholar 

  12. Rojas-Beltrán, J. A. et al. Identification of cytosolic Mg2+-dependent soluble inorganic pyrophosphatases in potato and phylogenetic analysis. Plant Mol. Biol. 39, 449–461 (1999)

    Article  Google Scholar 

  13. Plaxton, W. C. Plant Response to Stress: Biochemical Adaptations to Phosphate Deficiency (Marcel Decker, New York, 2004)

    Google Scholar 

  14. Gross, P. & ap Rees, T. Alkaline inorganic pyrophosphatase and starch synthesis in amyloplasts. Planta 167, 140–145 (1986)

    CAS  Article  Google Scholar 

  15. Jacob, J-L., Prevot, J-C., Clement-Vidal, A. & d’Auzac, J. Inorganic pyrophosphate metabolism in Hevea braziliensis latex. Characteristics of cytosolic alkaline pyrophosphatase. Plant Physiol. Biochem. 27, 355–364 (1989)

    CAS  Google Scholar 

  16. Geigenberger, P. et al. Overexpression of pyrophosphatase leads to increased sucrose degradation and starch synthesis, increased activities of enzymes for sucrose-starch interconversions, and increased levels of nucleotides in growing potato tubers. Planta 205, 428–437 (1998)

    CAS  Article  Google Scholar 

  17. Rajagopal, L., Clancy, A. & Rubens, C. E. A eukaryotic type serine/threonine kinase and phosphatase in Streptococcus agalactiae reversibly phosphorylate an inorganic pyrophosphatase and affect growth, cell segregation, and virulence. J. Biol. Chem. 278, 14429–14441 (2003)

    CAS  Article  Google Scholar 

  18. Rajagopal, L., Vo, A., Silvestroni, A. & Rubens, C. E. Regulation of purine biosynthesis by a eukaryotic-type kinase in Streptococcus agalactiae.. Mol. Microbiol. 56, 1329–1346 (2005)

    CAS  Article  Google Scholar 

  19. Vener, A. V., Smirnova, I. N. & Baykov, A. A. Phosphorylation of rat liver inorganic pyrophosphatase by ATP in the absence and in the presence of protein kinase. FEBS Lett. 264, 40–42 (1990)

    CAS  Article  Google Scholar 

  20. Chen, J. et al. Pyrophosphatase is essential for growth of Escherichia coli.. J. Bacteriol. 172, 5686–5689 (1990)

    CAS  Article  Google Scholar 

  21. Perez-Castineira, J. R., Lopez-Marques, R. L., Villalba, J. M., Losada, M. & Serrano, A. Functional complementation of yeast cytosolic pyrophosphatase by bacterial and plant H+-translocating pyrophosphatases. Proc. Natl Acad. Sci. USA 99, 15914–15919 (2002)

    ADS  CAS  Article  Google Scholar 

  22. Sonnewald, U. Expression of E. coli inorganic pyrophosphatase in transgenic plants alters photoassimilate partitioning. Plant J. 2, 571–581 (1992)

    CAS  PubMed  Google Scholar 

  23. Estruch, J., Kadwell, S., Merlin, E. & Crossland, L. Cloning and characterization of a maize pollen-specific calcium-dependent calmodulin-independent protein kinase. Proc. Natl Acad. Sci. USA 91, 8837–8841 (1994)

    ADS  CAS  Article  Google Scholar 

  24. Moutinho, A. et al. Antisense perturbation of protein function in living pollen tubes. Sex. Plant Reprod. 14, 101–104 (2001)

    CAS  Article  Google Scholar 

  25. Franklin-Tong, V. E., Hackett, G. & Hepler, P. K. Ratio-imaging of [Ca2+]i in the self-incompatibility response in pollen tubes of Papaver rhoeas.. Plant J. 12, 1375–1386 (1997)

    CAS  Article  Google Scholar 

  26. Thomas, S. G., Huang, S., Li, S., Staiger, C. J. & Franklin-Tong, V. E. Actin depolymerization is sufficient to induce programmed cell death in self-incompatible pollen. J. Cell Biol. 174, 221–229 (2006)

    CAS  Article  Google Scholar 

Download references


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 ( under accession codes AM162550 and AM162551. The authors declare no competing financial interests.

Author information

Authors and Affiliations


Corresponding author

Correspondence to Vernonica E. Franklin-Tong.

Supplementary information

Supplementary Figure Legends

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

Supplementary Figure 1

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

Supplementary Figure 2

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

Supplementary Figure 3

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

Supplementary Figure 4

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

Supplementary Methods

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

Rights and permissions

Reprints and Permissions

About this article

Cite this article

de Graaf, B., Rudd, J., Wheeler, M. et al. Self-incompatibility in Papaver targets soluble inorganic pyrophosphatases in pollen. Nature 444, 490–493 (2006).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing