Multiple avirulence loci and allele-specific effector recognition control the Pm3 race-specific resistance of wheat to powdery mildewopen

Plant Cell

Volumn 27, Issue 10, 2015, Pages 2991-3012

  Bourras, Salim ^c   McNally, Kaitlin Elyse ^c   Ben David, Roi ^a,c   Parlange, Francis ^c   Roffler, Stefan ^c   Praz, Coraline Rosalie ^c   Oberhaensli, Simone ^c   Menardo, Fabrizio ^c   Stirnweis, Daniel ^b,c   Frenkel, Zeev ^d   Schaefer, Luisa Katharina ^c   Flückiger, Simon ^c   Treier, Georges ^c   Herren, Gerhard ^c   Korol, Abraham B ^d   Wicker, Thomas ^c   Keller, Beat ^c  

^a VOLCANI CENTER   (Israel)

^b KWS SAAT SE   (Germany)

^c UNIVERSITY OF ZURICH   (Switzerland)

^d UNIVERSITY OF HAIFA   (Israel)

Author keywords

[No Author keywords available]

Indexed keywords

PLANT PROTEIN;

ALLELE; AMINO ACID SEQUENCE; ASCOMYCETES; BIOLOGICAL MODEL; CROSS BREEDING; DISEASE RESISTANCE; DNA SEQUENCE; GENE EXPRESSION; GENETIC POLYMORPHISM; GENETICS; IMMUNOLOGY; METABOLISM; MICROBIOLOGY; MOLECULAR EVOLUTION; MOLECULAR GENETICS; PATHOGENICITY; PLANT DISEASE; PLANT LEAF; SEQUENCE ALIGNMENT; SPECIES DIFFERENCE; TOBACCO; VIRULENCE; WHEAT;

ALLELES; AMINO ACID SEQUENCE; ASCOMYCOTA; CROSSES, GENETIC; DISEASE RESISTANCE; EVOLUTION, MOLECULAR; GENE EXPRESSION; MODELS, GENETIC; MOLECULAR SEQUENCE ANNOTATION; PLANT DISEASES; PLANT LEAVES; PLANT PROTEINS; POLYMORPHISM, GENETIC; SEQUENCE ALIGNMENT; SEQUENCE ANALYSIS, DNA; SPECIES SPECIFICITY; TOBACCO; TRITICUM; VIRULENCE;

EID: 84946735511     PISSN: 10404651     EISSN: 1532298X     Source Type: Journal    
DOI: 10.1105/tpc.15.00171     Document Type: Article

References (93)

1. Abascal, F., Zardoya, R., and Telford, M.J. (2010). TranslatorX: multiple alignment of nucleotide sequences guided by amino acid translations. Nucleic Acids Res. 38: W7–W13.
2. Allen, R.L., Bittner-Eddy, P.D., Grenville-Briggs, L.J., Meitz, J.C., Rehmany, A.P., Rose, L.E., and Beynon, J.L. (2004). Host-parasite coevolutionary conflict between Arabidopsis and downy mildew. Science 306: 1957–1960.
3. Aluko, G., Martinez, C., Tohme, J., Castano, C., Bergman, C., and Oard, J.H. (2004). QTL mapping of grain quality traits from the interspecific cross Oryza sativa x O. glaberrima. Theor. Appl. Genet. 109: 630–639.
4. Anderson, P.A., Lawrence, G.J., Morrish, B.C., Ayliffe, M.A., Finnegan, E.J., and Ellis, J.G. (1997). Inactivation of the flax rust resistance gene M associated with loss of a repeated unit within the leucine-rich repeat coding region. Plant Cell 9: 641–651.
5. Bakkeren, G., and Valent, B. (2014). Do pathogen effectors play peek-a-boo? Front. Plant Sci. 5:731
6. Balesdent, M.H., Attard, A., Kühn, M.L., and Rouxel, T. (2002). New avirulence genes in the phytopathogenic fungus Leptosphaeria maculans. Phytopathology 92: 1122–1133.
7. Batagelj, V., and Mrvar, A. (2003). Graph Drawing Software: Pajek Analysis and Visualization of Large Networks. (Berlin: Springer).
8. Beyer, A., Bandyopadhyay, S., and Ideker, T. (2007). Integrating physical and genetic maps: from genomes to interaction networks. Nat. Rev. Genet. 8: 699–710.
9. Bhullar, N.K., Street, K., Mackay, M., Yahiaoui, N., and Keller, B.(2009). Unlocking wheat genetic resources for the molecular identification of previously undescribed functional alleles at the Pm3 resistance locus. Proc. Natl. Acad. Sci. USA 106: 9519–9524.
10. Bhullar, N.K., Zhang, Z., Wicker, T., and Keller, B. (2010). Wheat gene bank accessions as a source of new alleles of the powdery mildew resistance gene Pm3: a large scale allele mining project. BMC Plant Biol. 10: 88.
11. Boller, T., and He, S.Y. (2009). Innate immunity in plants: an arms race between pattern recognition receptors in plants and effectors in microbial pathogens. Science 324: 742–744.
12. Brown, J.K., and Simpson, C.G. (1994). Genetic analysis of DNA fingerprints and virulences in Erysiphe graminis f.sp. hordei. Curr. Genet. 26: 172–178.
13. Brown, J.K.M., and Jessop, A.C. (1995). Genetics of avirulences in Erysiphe graminis f.sp. hordei. Plant Pathol. 44: 1039–1049.
14. Brown, J.K.M., and Wolfe, M.S. (1990). Structure and evolution of a population of Erysiphe graminis f. sp. hordei. Plant Pathol. 39: 376–390.
15. Brown, J.K.M., Le Boulaire, S., and Evans, N. (1996). Genetics of responses to morpholine-type fungicides and of avirulences in Erysiphe graminis f. sp. hordei. Eur. J. Plant Pathol. 102: 479–490.
16. Brunner, S., Hurni, S., Streckeisen, P., Mayr, G., Albrecht, M., Yahiaoui, N., and Keller, B. (2010). Intragenic allele pyramiding combines different specificities of wheat Pm3 resistance alleles. Plant J. 64: 433–445.
17. Bustin, S.A., Benes, V., Garson, J.A., Hellemans, J., Huggett, J., Kubista, M., Mueller, R., Nolan, T., Pfaffl, M.W., Shipley, G.L., Vandesompele, J., and Wittwer, C.T. (2009). The MIQE guidelines: minimum information for publication of quantitative real-time PCR experiments. Clin.Chem. 55: 611–622.
18. Caffier, V., de Vallavieille-Pope, C., and Brown, J.K.M. (1996). Segregation of avirulences and genetic basis of infection types in Erysiphe graminis f.sp. hordei. Phytopathology 86: 1112–1121.
19. Catanzariti, A.M., Dodds, P.N., Ve, T., Kobe, B., Ellis, J.G., and Staskawicz, B.J. (2010). The AvrM effector from flax rust has a structured C-terminal domain and interacts directly with the M resistance protein. Mol. Plant Microbe Interact. 23: 49–57.
20. Cesari, S., et al. (2013). The rice resistance protein pair RGA4/RGA5 recognizes the Magnaporthe oryzae effectors AVR-Pia and AVR1- CO39 by direct binding. Plant Cell 25: 1463–1481.
21. Chen, X., and Yang, J.Y. (2010). Constructing consensus genetic maps in comparative analysis. J. Comput. Biol. 17: 1561–1573.
22. Dodds, P.N., Lawrence, G.J., Catanzariti, A.M., Ayliffe, M.A., and Ellis, J.G. (2004). The Melampsora lini AvrL567 avirulence genes are expressed in haustoria and their products are recognized inside plant cells. Plant Cell 16: 755–768.
23. Dodds, P.N., Lawrence, G.J., Catanzariti, A.M., Teh, T., Wang, C.I.A., Ayliffe, M.A., Kobe, B., and Ellis, J.G. (2006). Direct protein interaction underlies gene-for-gene specificity and coevolution of the flax resistance genes and flax rust avirulence genes. Proc. Natl. Acad. Sci. USA 103: 8888–8893.
24. Dodds, P.N., Rafiqi, M., Gan, P.H., Hardham, A.R., Jones, D.A., and Ellis, J.G. (2009). Effectors of biotrophic fungi and oomycetes: pathogenicity factors and triggers of host resistance. New Phytol. 183: 993–1000.
25. Dugdale, B., Mortimer, C.L., Kato, M., James, T.A., Harding, R.M., and Dale, J.L. (2014). Design and construction of an in-plant activation cassette for transgene expression and recombinant protein production in plants. Nat. Protoc. 9: 1010–1027.
26. Edgar, R.C. (2004). MUSCLE: multiple sequence alignment with high accuracy and high throughput. Nucleic Acids Res. 32: 1792–1797.
27. Ellis, J.G., Dodds, P.N., and Lawrence, G.J. (2007). Flax rust resistance gene specificity is based on direct resistance-avirulence protein interactions. Annu. Rev. Phytopathol. 45: 289–306.
28. Ellis, J.G., Lawrence, G.J., Luck, J.E., and Dodds, P.N. (1999). Identification of regions in alleles of the flax rust resistance gene L that determine differences in gene-for-gene specificity. Plant Cell 11: 495–506.
29. Flor, H.H. (1956). The complementary genic systems in flax and flax rust. Adv. Genet. 8: 29–54.
30. Flor, H.H. (1971). Current status of the gene-for-gene concept. Annu. Rev. Phytopathol. 9: 275–296.
31. Frenkel, Z., Paux, E., Mester, D., Feuillet, C., and Korol, A. (2010). LTC: a novel algorithm to improve the efficiency of contig assembly for physical mapping in complex genomes. BMC Bioinformatics 11: 584.
32. Fudal, I., Ross, S., Gout, L., Blaise, F., Kuhn, M.L., Eckert, M.R., Cattolico, L., Bernard-Samain, S., Balesdent, M.H., and Rouxel, T. (2007). Heterochromatin-like regions as ecological niches for avirulence genes in the Leptosphaeria maculans genome: mapbased cloning of AvrLm6. Mol. Plant Microbe Interact. 20: 459–470.
33. Gawehns, F., Houterman, P.M., Ichou, F.A., Michielse, C.B., Hijdra, M., Cornelissen, B.J.C., Rep, M., and Takken, F.L.W. (2014). The Fusarium oxysporum effector Six6 contributes to virulence and suppresses I-2-mediated cell death. Mol. Plant Microbe Interact. 27: 336–348.
34. Gijzen, M., Ishmael, C., and Shrestha, S.D. (2014). Epigenetic control of effectors in plant pathogens. Front. Plant Sci. 5: 638.
35. Godfrey, D., Böhlenius, H., Pedersen, C., Zhang, Z., Emmersen, J., and Thordal-Christensen, H. (2010). Powdery mildew fungal effector candidates share N-terminal Y/F/WxC-motif. BMC Genomics 11: 317.
36. Hall, S.A., Allen, R.L., Baumber, R.E., Baxter, L.A., Fisher, K., Bittner-Eddy, P.D., Rose, L.E., Holub, E.B., and Beynon, J.L. (2009). Maintenance of genetic variation in plants and pathogens involves complex networks of gene-for-gene interactions. Mol. Plant Pathol. 10: 449–457.
37. He, C., Holme, J., and Anthony, J. (2014). SNP genotyping: the KASP assay. Methods Mol. Biol. 1145: 75–86.
38. Houterman, P.M., Cornelissen, B.J.C., and Rep, M. (2008). Suppression of plant resistance gene-based immunity by a fungal effector. PLoS Pathog. 4: e1000061.
39. Howles, P., Lawrence, G., Finnegan, J., McFadden, H., Ayliffe, M., Dodds, P., and Ellis, J. (2005). Autoactive alleles of the flax L6 rust resistance gene induce non-race-specific rust resistance associated with the hypersensitive response. Mol. Plant Microbe Interact. 18: 570–582.
40. Huang, J., Si, W., Deng, Q., Li, P., and Yang, S. (2014). Rapid evolution of avirulence genes in rice blast fungus Magnaporthe oryzae. BMC Genet. 15: 45.
41. Jones, D.A. (1988a). Genes for resistance to flax rust in the flax cultivars Towner and Victory and the genetics of pathogenicity in flax rust to the L8 gene for resistance. Phytopathology 78: 338–341.
42. Jones, D.A. (1988b). Genetic properties on inhibitor genes in flax rust that alter avirulence to virulence on flax. Phytopathology 78:342–344.
43. Jones, J.D.G., and Dangl, J.L. (2006). The plant immune system. Nature 444: 323–329.
44. Kanzaki, H., Yoshida, K., Saitoh, H., Fujisaki, K., Hirabuchi, A., Alaux, L., Fournier, E., Tharreau, D., and Terauchi, R. (2012). Arms race co-evolution of Magnaporthe oryzae AVR-Pik and rice Pik genes driven by their physical interactions. Plant J. 72: 894–907.
45. Krasileva, K.V., Dahlbeck, D., and Staskawicz, B.J. (2010). Activation of an Arabidopsis resistance protein is specified by the in planta association of its leucine-rich repeat domain with the cognate oomycete effector. Plant Cell 22: 2444–2458. Lander, E.S., Green, P., Abrahamson, J., Barlow, A., Daly, M.J
46. Lincoln, S.E., and Newberg, L.A. (1987). MAPMAKER: an interactive computer package for constructing primary genetic linkage maps of experimental and natural populations. Genomics 1: 174–181. Erratum. Genomics 93: 398.
47. Larkin, M.A., et al. (2007). Clustal W and Clustal X version 2.0. Bioinformatics 23: 2947–2948.
48. Lawrence, G.J., Mayo, G.M.E., and Shepherd, K.W. (1981). Interactions between genes controlling pathogenicity in the flax rust fungus. Phytopathology 71: 12–19.
49. Lévesque, C.A., et al. (2010). Genome sequence of the necrotrophic plant pathogen Pythium ultimum reveals original pathogenicity mechanisms and effector repertoire. Genome Biol. 11: R73.
50. Ma, L., et al. (2015). The AVR2-SIX5 gene pair is required to activate I-2-mediated immunity in tomato. New Phytol. 208: 507–518.
51. Ma, L., Lukasik, E., Gawehns, F., and Takken, F.L. (2012). The use of agroinfiltration for transient expression of plant resistance and fungal effector proteins in Nicotiana benthamiana leaves. In Plant Fungal Pathogens, M.D. Bolton and B.P.H.J. Thomma, eds (Humana Press), pp. 61–74.
52. Marone, D., Russo, M.A., Laidò, G., De Leonardis, A.M., and Mastrangelo, A.M. (2013). Plant nucleotide binding site-leucine-rich repeat (NBS-LRR) genes: active guardians in host defense responses. Int. J. Mol. Sci. 14: 7302–7326.
53. Moffett, P., Farnham, G., Peart, J., and Baulcombe, D.C. (2002). Interaction between domains of a plant NBS-LRR protein in disease resistance-related cell death. EMBO J. 21: 4511–4519.
54. Nielsen, R., and Yang, Z. (1998). Likelihood models for detecting positively selected amino acid sites and applications to the HIV-1 envelope gene. Genetics 148: 929–936.
55. Parlange, F., Oberhaensli, S., Breen, J., Platzer, M., Taudien, S., Simková, H., Wicker, T., Dolezˇel, J., and Keller, B. (2011). A major invasion of transposable elements accounts for the large size of the Blumeria graminis f.sp. tritici genome. Funct. Integr. Genomics 11: 671–677.
56. Parlange, F., Roffler, S., Menardo, F., Ben-David, R., Bourras, S., McNally, K.E., Oberhaensli, S., Stirnweis, D., Buchmann, G., Wicker, T., and Keller, B. (2015). Genetic and molecular characterization of a locus involved in avirulence of Blumeria graminis f. sp. tritici on wheat Pm3 resistance alleles. Fungal Genet. Biol. 82: 181–192.
57. Parniske, M., Hammond-Kosack, K.E., Golstein, C., Thomas, C.M., Jones, D.A., Harrison, K., Wulff, B.B., and Jones, J.D. (1997). Novel disease resistance specificities result from sequence exchange between tandemly repeated genes at the Cf-4/9 locus of tomato. Cell 91: 821–832.
58. Petersen, T.N., Brunak, S., von Heijne, G., and Nielsen, H. (2011). SignalP 4.0: discriminating signal peptides from transmembrane regions. Nat. Methods 8: 785–786.
59. Raffaele, S., et al. (2010). Genome evolution following host jumps in the Irish potato famine pathogen lineage. Science 330: 1540–1543.
60. Rafiqi, M., Ellis, J.G., Ludowici, V.A., Hardham, A.R., and Dodds, P.N. (2012). Challenges and progress towards understanding the role of effectors in plant-fungal interactions. Curr. Opin. Plant Biol. 15: 477–482.
61. Ravensdale, M., Bernoux, M., Ve, T., Kobe, B., Thrall, P.H., Ellis, J.G., and Dodds, P.N. (2012). Intramolecular interaction influences binding of the Flax L5 and L6 resistance proteins to their AvrL567 ligands. PLoS Pathog. 8: e1003004.
62. Ravensdale, M., Nemri, A., Thrall, P.H., Ellis, J.G., and Dodds, P.N. (2011). Co-evolutionary interactions between host resistance and pathogen effector genes in flax rust disease. Mol. Plant Pathol. 12: 93–102.
63. Ridout, C.J., Skamnioti, P., Porritt, O., Sacristan, S., Jones, J.D.G., and Brown, J.K.M. (2006). Multiple avirulence paralogues in cereal powdery mildew fungi may contribute to parasite fitness and defeat of plant resistance. Plant Cell 18: 2402–2414.
64. Rose, L.E., Bittner-Eddy, P.D., Langley, C.H., Holub, E.B., Michelmore, R.W., and Beynon, J.L. (2004). The maintenance of extreme amino acid diversity at the disease resistance gene, RPP13, in Arabidopsis thaliana. Genetics 166: 1517–1527.
65. Schweizer, P., Pokorny, J., Abderhalden, O., and Dudler, R. (1999). A transient assay system for the functional assessment of defenserelated genes in wheat. Mol. Plant Microbe Interact. 12: 647–654.
66. Seeholzer, S., Tsuchimatsu, T., Jordan, T., Bieri, S., Pajonk, S., Yang, W., Jahoor, A., Shimizu, K.K., Keller, B., and Schulze- Lefert, P. (2010). Diversity at the Mla powdery mildew resistance locus from cultivated barley reveals sites of positive selection. Mol. Plant Microbe Interact. 23: 497–509.
67. Sela, H., Spiridon, L.N., Ashkenazi, H., Bhullar, N.K., Brunner, S., Petrescu, A.J., Fahima, T., Keller, B., and Jordan, T. (2014). Three-dimensional modeling and diversity analysis reveals distinct AVR recognition sites and evolutionary pathways in wild and domesticated wheat Pm3 R genes. Mol. Plant Microbe Interact. 27: 835–845.
68. Sohn, K.H., Lei, R., Nemri, A., and Jones, J.D. (2007). The downy mildew effector proteins ATR1 and ATR13 promote disease susceptibility in Arabidopsis thaliana. Plant Cell 19: 4077–4090.
69. Sonnhammer, E.L., and Durbin, R. (1995). A dot-matrix program with dynamic threshold control suited for genomic DNA and protein sequence analysis. Gene 167: GC1–GC10.
70. Spanu, P.D., et al. (2010). Genome expansion and gene loss in powdery mildew fungi reveal tradeoffs in extreme parasitism. Science 330: 1543–1546.
71. Srichumpa, P., Brunner, S., Keller, B., and Yahiaoui, N. (2005). Allelic series of four powdery mildew resistance genes at the Pm3 locus in hexaploid bread wheat. Plant Physiol. 139: 885–895.
72. Stamatakis, A. (2014). RAxML version 8: a tool for phylogenetic analysis and post-analysis of large phylogenies. Bioinformatics 30: 1312–1313.
73. Steinbrenner, A.D., Goritschnig, S., and Staskawicz, B.J. (2015). Recognition and activation domains contribute to allele-specificresponses of an Arabidopsis NLR receptor to an oomycete effector protein. PLoS Pathog. 11: e1004665.
74. Stirnweis, D., Milani, S.D., Brunner, S., Herren, G., Buchmann, G., Peditto, D., Jordan, T., and Keller, B. (2014b). Suppression among alleles encoding nucleotide-binding-leucine-rich repeat resistance proteins interferes with resistance in F1 hybrid and allele-pyramided wheat plants. Plant J. 79: 893–903.
75. Stirnweis, D., Milani, S.D., Jordan, T., Keller, B., and Brunner, S. (2014a). Substitutions of two amino acids in the nucleotide-binding site domain of a resistance protein enhance the hypersensitive response and enlarge the PM3F resistance spectrum in wheat. Mol. Plant Microbe Interact. 27: 265–276.
76. Sun, Q., Collins, N.C., Ayliffe, M., Smith, S.M., Drake, J., Pryor, T., and Hulbert, S.H. (2001). Recombination between paralogues at the Rp1 rust resistance locus in maize. Genetics 158: 423– 438.
77. Takagi, H., et al. (2013). QTL-seq: rapid mapping of quantitative trait loci in rice by whole genome resequencing of DNA from two bulked populations. Plant J. 74: 174–183.
78. Terauchi, R., Yoshida, K., Saitoh, H., Kanzaki, H., Okuyama, Y., Fujisaki, K., Miya, A., Abe, A., Tamiru, M., and Tosa, Y. (2011). Studying genome-wide DNA polymorphisms to understand Magnaporthe–rice interactions. Australas. Plant Pathol. 40: 328–334.
79. van der Lee, T., Robold, A., Testa, A., van ’t Klooster, J.W., and Govers, F. (2001). Mapping of avirulence genes in Phytophthora infestans with amplified fragment length polymorphism markers selected by bulked segregant analysis. Genetics 157: 949–956.
80. Vleeshouwers, V.G., and Oliver, R.P. (2014). Effectors as tools in disease resistance breeding against biotrophic, hemibiotrophic, and necrotrophic plant pathogens. Mol. Plant Microbe Interact. 27:196–206.
81. Vleeshouwers, V.G.A.A., Raffaele, S., Vossen, J.H., Champouret, N., Oliva, R., Segretin, M.E., Rietman, H., Cano, L.M., Lokossou, A., Kessel, G., Pel, M.A., and Kamoun, S. (2011). Understanding and exploiting late blight resistance in the age of effectors. Annu. Rev. Phytopathol. 49: 507–531.
82. Wang, C.I.A., et al. (2007). Crystal structures of flax rust avirulence proteins AvrL567-A and -D reveal details of the structural basis for flax disease resistance specificity. Plant Cell 19:2898–2912.
83. Weadick, C.J., and Chang, B.S. (2012). An improved likelihood ratio test for detecting site-specific functional divergence among clades of protein-coding genes. Mol. Biol. Evol. 29: 1297–1300.
84. Wicker, T., et al. (2013). The wheat powdery mildew genome shows the unique evolution of an obligate biotroph. Nat. Genet. 45:1092–1096.
85. Williams, S.J., Sornaraj, P., deCourcy-Ireland, E., Menz, R.I., Kobe, B., Ellis, J.G., Dodds, P.N., and Anderson, P.A. (2011). An autoactive mutant of the M flax rust resistance protein has a preference for binding ATP, whereas wild-type M protein binds ADP. Mol. Plant Microbe Interact. 24: 897–906.
86. Wu, Y., Close, T.J., and Lonardi, S. (2008). On the accurate construction of consensus genetic maps. Comput. Syst. Bioinformatics Conf. 7: 285–296.
87. Yahiaoui, N., Brunner, S., and Keller, B. (2006). Rapid generation of new powdery mildew resistance genes after wheat domestication. Plant J. 47: 85–98.
88. Yahiaoui, N., Kaur, N., and Keller, B. (2009). Independent evolution of functional Pm3 resistance genes in wild tetraploid wheat and domesticated bread wheat. Plant J. 57: 846–856.
89. Yahiaoui, N., Srichumpa, P., Dudler, R., and Keller, B. (2004). Genome analysis at different ploidy levels allows cloning of the powdery mildew resistance gene Pm3b from hexaploid wheat. Plant J. 37: 528–538.
90. Yang, Z. (2007). PAML 4: phylogenetic analysis by maximum likelihood. Mol. Biol. Evol. 24: 1586–1591.
91. Yang, Z., Nielsen, R., Goldman, N., and Pedersen, A.M.K. (2000). Codon-substitution models for heterogeneous selection pressure at amino acid sites. Genetics 155: 431–449.
92. Yang, Z., Wong, W.S., and Nielsen, R. (2005). Bayes empirical bayes inference of amino acid sites under positive selection. Mol. Biol. Evol. 22: 1107–1118.
93. Yoshida, K., Saitoh, H., Fujisawa, S., Kanzaki, H., Matsumura, H., Yoshida, K., Tosa, Y., Chuma, I., Takano, Y., Win, J., Kamoun, S., and Terauchi, R. (2009). Association genetics reveals three novel avirulence genes from the rice blast fungal pathogen Magnaporthe oryzae. Plant Cell 21: 1573–1591.