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The structural basis for activation of plant immunity by bacterial effector protein AvrPto


Pathogenic microbes use effectors to enhance susceptibility in host plants. However, plants have evolved a sophisticated immune system to detect these effectors using cognate disease resistance proteins1, a recognition that is highly specific, often elicits rapid and localized cell death, known as a hypersensitive response, and thus potentially limits pathogen growth2,3,4,5. Despite numerous genetic and biochemical studies on the interactions between pathogen effector proteins and plant resistance proteins, the structural bases for such interactions remain elusive. The direct interaction between the tomato protein kinase Pto and the Pseudomonas syringae effector protein AvrPto is known to trigger disease resistance and programmed cell death6,7 through the nucleotide-binding site/leucine-rich repeat (NBS-LRR) class of disease resistance protein Prf8. Here we present the crystal structure of an AvrPto–Pto complex. Contrary to the widely held hypothesis that AvrPto activates Pto kinase activity, our structural and biochemical analyses demonstrated that AvrPto is an inhibitor of Pto kinase in vitro. The AvrPto–Pto interaction is mediated by the phosphorylation-stabilized P+1 loop and a second loop in Pto, both of which negatively regulate the Prf-mediated defences in the absence of AvrPto in tomato plants. Together, our results show that AvrPto derepresses host defences by interacting with the two defence-inhibition loops of Pto.

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Figure 1: Bipartite AvrPto–Pto interfaces.
Figure 2: The active conformation of Pto is important for AvrPto binding.
Figure 3: Mutations in the two AvrPto–Pto interfaces trigger a CGF hypersensitive response in N. benthamiana.
Figure 4: AvrPto inhibits the kinase activity of Pto in vitro.

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  1. Flor, H. H. Current status of the gene-for-gene concept. Annu. Rev. Phytopathol. 9, 275–296 (1971)

    Article  Google Scholar 

  2. Belkhadir, Y., Subramaniam, R. & Dangl, J. L. Plant disease resistance protein signaling: NBS-LRR proteins and their partners. Curr. Opin. Plant Biol. 7, 391–399 (2004)

    Article  CAS  Google Scholar 

  3. Chisholm, S. T., Coaker, G., Day, B. & Staskawicz, B. J. Host–microbe interactions: shaping the evolution of the plant immune response. Cell 124, 803–814 (2006)

    Article  CAS  Google Scholar 

  4. Innes, R. W. Guarding the goods. New insights into the central alarm system of plants. Plant Physiol. 135, 695–701 (2004)

    Article  CAS  Google Scholar 

  5. Pedley, K. F. & Martin, G. B. Molecular basis of Pto-mediated resistance to bacterial speck disease in tomato. Annu. Rev. Phytopathol. 41, 215–243 (2003)

    Article  CAS  Google Scholar 

  6. Scofield, S. R. et al. Molecular basis of gene-for-gene specificity in bacterial speck disease of tomato. Science 274, 2063–2065 (1996)

    Article  ADS  CAS  Google Scholar 

  7. Tang, X. et al. Initiation of plant disease resistance by physical interaction of AvrPto and Pto kinase. Science 274, 2060–2063 (1996)

    Article  ADS  CAS  Google Scholar 

  8. Salmeron, J. M. et al. Tomato Prf is a member of the leucine-rich repeat class of plant disease resistance genes and lies embedded within the Pto kinase gene cluster. Cell 86, 123–133 (1996)

    Article  CAS  Google Scholar 

  9. He, S. Y., Nomura, K. & Whittam, T. Type III secretion in mammalian and plant pathogens. Biochim. Biophys. Acta 1694, 181–206 (2004)

    Article  CAS  Google Scholar 

  10. Galan, J. E. Salmonella interactions with host cells: type III secretion at work. Annu. Rev. Cell Dev. Biol. 17, 53–86 (2001)

    Article  CAS  Google Scholar 

  11. Hueck, C. J. Type III protein secretion systems in bacterial pathogens of animals and plants. Microbiol. Mol. Biol. Rev. 62, 379–433 (1998)

    Article  CAS  Google Scholar 

  12. Kim, Y. J., Lin, N. C. & Martin, G. B. Two distinct Pseudomonas effector proteins interact with the Pto kinase and activate plant immunity. Cell 109, 589–598 (2002)

    Article  CAS  Google Scholar 

  13. Mucyn, T. S. et al. The tomato NBARC-LRR protein Prf interacts with Pto kinase in vivo to regulate specific plant immunity. Plant Cell 18, 2792–2806 (2006)

    Article  CAS  Google Scholar 

  14. Rathjen, J. P., Chang, J. H., Staskawicz, B. J. & Michelmore, R. W. Constitutively active Pto induces a Prf-dependent hypersensitive response in the absence of AvrPto. EMBO J. 18, 3232–3240 (1999)

    Article  CAS  Google Scholar 

  15. Wu, A. J., Andriotis, V. M., Durrant, M. C. & Rathjen, J. P. A patch of surface-exposed residues mediates negative regulation of immune signaling by tomato Pto kinase. Plant Cell 16, 2809–2821 (2004)

    Article  CAS  Google Scholar 

  16. He, P. et al. Specific bacterial suppressors of MAMP signaling upstream of MAPKKK in Arabidopsis innate immunity. Cell 125, 563–575 (2006)

    Article  CAS  Google Scholar 

  17. Wulf, J., Pascuzzi, P. E., Fahmy, A., Martin, G. B. & Nicholson, L. K. The solution structure of type III effector protein AvrPto reveals conformational and dynamic features important for plant pathogenesis. Structure 12, 1257–1268 (2004)

    Article  CAS  Google Scholar 

  18. Chang, J. H. et al. Functional analyses of the Pto resistance gene family in tomato and the identification of a minor resistance determinant in a susceptible haplotype. Mol. Plant Microbe Interact. 15, 281–291 (2002)

    Article  CAS  Google Scholar 

  19. Frederick, R. D., Thilmony, R. L., Sessa, G. & Martin, G. B. Recognition specificity for the bacterial avirulence protein AvrPto is determined by Thr-204 in the activation loop of the tomato Pto kinase. Mol. Cell 2, 241–245 (1998)

    Article  CAS  Google Scholar 

  20. Riely, B. K. & Martin, G. B. Ancient origin of pathogen recognition specificity conferred by the tomato disease resistance gene Pto. Proc. Natl Acad. Sci. USA 98, 2059–2064 (2001)

    Article  ADS  CAS  Google Scholar 

  21. Huse, M. & Kuriyan, J. The conformational plasticity of protein kinases. Cell 109, 275–282 (2002)

    Article  CAS  Google Scholar 

  22. Nolen, B., Taylor, S. & Ghosh, G. Regulation of protein kinases; controlling activity through activation segment conformation. Mol. Cell 15, 661–675 (2004)

    Article  CAS  Google Scholar 

  23. Sessa, G., D'Ascenzo, M. & Martin, G. B. Thr38 and Ser198 are Pto autophosphorylation sites required for the AvrPto–Pto-mediated hypersensitive response. EMBO J. 19, 2257–2269 (2000)

    Article  CAS  Google Scholar 

  24. Bossemeyer, D., Engh, R. A., Kinzel, V., Ponstingl, H. & Huber, R. Phosphotransferase and substrate binding mechanism of the cAMP-dependent protein kinase catalytic subunit from porcine heart as deduced from the 2.0 Å structure of the complex with Mn2+ adenylyl imidodiphosphate and inhibitor peptide PKI(5–24). EMBO J. 12, 849–859 (1993)

    Article  CAS  Google Scholar 

  25. Stebbins, C. E. & Galan, J. E. Maintenance of an unfolded polypeptide by a cognate chaperone in bacterial type III secretion. Nature 414, 77–81 (2001)

    Article  ADS  CAS  Google Scholar 

  26. Otwinowski, Z. & Minor, W. Processing of X-ray diffraction data collected in oscillation mode. Methods Enzymol. 276, 307–326 (1997)

    Article  CAS  Google Scholar 

  27. Terwilliger, T. C. SOLVE and RESOLVE: automated structure solution and density modification. Methods Enzymol. 374, 22–37 (2003)

    Article  CAS  Google Scholar 

  28. Jones, T. A., Zou, J. Y., Cowan, S. W. & Kjeldgaard, M. Improved methods for building protein models in electron density maps and the location of errors in these models. Acta Crystallogr. A 47, 110–119 (1997)

    Article  Google Scholar 

  29. Murshudov, G. N., Vagin, A. A. & Dodson, E. J. Refinement of macromolecular structures by the maximum-likelihood method. Acta Crystallogr. D53, 240–255 (1997)

    CAS  Google Scholar 

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We thank R. Innes, S. He and X. Tang for critical reading and comments on our manuscript, and Y. Dong and P. Liu at the BSRF (Beijing, China) beam line 3W1A for assistance with the data collection. We are grateful to X. Liu and L. Ma for help with SPR assay. This research is funded by a Chinese Ministry of Science and Technology grant to J.C. and to J.-M.Z.

Author Contributions W.X. purified, crystallized and determined the structure and performed biochemical assays; Y.Z. performed Agrobacterium-mediated transient expression; Q.L., Q. Huang and Q. Hao determined structure; J.L. and X.L. purified proteins; S.C. performed the mass spectrometry assay; J.-W.W. measured the half-maximal inhibitory concentration; R.B. and L.Z. were involved in the study design; and J.-M.Z. and J.C. designed the study, analysed data and prepared the manuscript.

The atomic coordinates and structure factors of the AvrPto–Pto complex have been deposited in the RCSB Protein Data Bank under accession code 2QKW.

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Correspondence to Jijie Chai.

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Xing, W., Zou, Y., Liu, Q. et al. The structural basis for activation of plant immunity by bacterial effector protein AvrPto. Nature 449, 243–247 (2007).

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