15. Russmann H, Shams H, Poblete F, Fu Y, Galan JE, et al. (1998) Delivery of epitopes by the Salmonella type III secretion system for vaccine development. Science 281: 565–568. 16. Wieser A, Magistro G, Norenberg D, Hoffmann C, Schubert S (2012) First multi-epitope subunit vaccine against extraintestinal pathogenic Escherichia coli delivered by a bacterial type-3 secretion system (T3SS). Int J Med Microbiol 302: 10–18. 17. Dale C, Plague GR, Wang B, Ochman H, Moran (2002) Type III secretion systems and the evolution of mutualistic endosymbiosis. Proc Natl Acad Sci U S A 99: 12397–12402. 18. Freiberg C, Fellay R, Bairoch A, Broughton WJ, Rosenthal A, et al. (1997) Molecular basis of symbiosis between Rhizobium and legumes. Nature 387: 394–401. 19. Lackner G, Moebius N, Hertweck C (2011) Endofungal bacterium controls its host by an hrp type III secretion system. ISME J 5: 252–261. 20. Horn M, Collingro A, Schmitz-Esser S, Beier CL, Purkhold U, et al. (2004) Illuminating the evolutionary history of chlamydiae. Science 304: 728–730. 21. Desvaux M, Hebraud M, Talon R, Henderson IR (2009) Secretion and subcellular localizations of bacterial proteins: a semantic awareness issue. Trends Microbiol 17: 139–145. 22. Michiels T, Vanooteghem JC, Lambert de Rouvroit C, China B, Gustin A, et al. (1991) Analysis of virC, an operon involved in the secretion of Yop proteins by Yersinia enterocolitica. J Bacteriol 173: 4994–5009. 23. Huang HC, He SY, Bauer DW, Collmer A (1992) The Pseudomonas syringae pv. syringae 61 hrpH product, an envelope protein required for elicitation of the hypersensitive response in plants. J Bacteriol 174: 6878–6885. 24. Charkowski AO, Huang HC, Collmer A (1997) Altered localization of HrpZ in Pseudomonas syringae pv. syringae hrp mutants suggests that different components of the type III secretion pathway control protein translocation across the inner and outer membranes of gram-negative bacteria. J Bacteriol 179: 3866–3874. 25. Korotkov KV, Gonen T, Hol WGJ (2011) Secretins: dynamic channels for protein transport across membranes. Trends Biochem Sci 36: 433–443. 26. Kubori T, Sukhan A, Aizawa SI, Galan JE (2000) Molecular characterization and assembly of the needle complex of the Salmonella typhimurium type III protein secretion system. Proc Natl Acad Sci U S A 97: 10225–10230. 27. Kubori T, Matsushima Y, Nakamura D, Uralil J, Lara-Tejero M, et al. (1998) Supramolecular structure of the Salmonella typhimurium type III protein secretion system. Science 280: 602–605. 28. Hoiczyk E, Blobel G (2001) Polymerization of a single protein of the pathogen Yersinia enterocolitica into needles punctures eukaryotic cells. Proc Natl Acad Sci U S A 98: 4669–4674. 29. Kimbrough TG, Miller SI (2000) Contribution of Salmonella typhimurium type III secretion components to needle complex formation. Proc Natl Acad Sci U S A 97: 11008–11013. 30. Roine E, Saarinen J, Kalkkinen N, Romantschuk M (1997) Purified HrpA of Pseudomonas syringae pv. tomato DC3000 reassembles into pili. FEBS Lett 417: 168–172. 31. Van Gijsegem F, Vasse J, Camus JC, Marenda M, Boucher C (2000) Ralstonia solanacearum produces hrp-dependent pili that are required for PopA secretion but not for attachment of bacteria to plant cells. Mol Microbiol 36: 249–260. 32. He SY, Jin Q (2003) The Hrp pilus: learning from flagella. Curr Opin Microbiol 6: 15–19. 33. Menard R, Sansonetti P, Parsot C (1994) The secretion of the Shigella flexneri Ipa invasins is activated by epithelial cells and controlled by IpaB and IpaD. EMBO J 13: 5293–5302. 34. Picking WL, Nishioka H, Hearn PD, Baxter MA, Harrington AT, et al. (2005) IpaD of Shigella flexneri is independently required for regulation of Ipa protein secretion and efficient insertion of IpaB and IpaC into host membranes. Infect Immun 73: 1432–1440. 35. Hakansson S, Schesser K, Persson C, Galyov EE, Rosqvist R, et al. (1996) The YopB protein of Yersinia pseudotuberculosis is essential for the translocation of Yop effector proteins across the target cell plasma membrane and displays a contact-dependent membrane disrupting activity. EMBO J 15: 5812–5823. 36. Vogler AP, Homma M, Irikura VM, Macnab RM (1991) Salmonella typhimurium mutants defective in flagellar filament regrowth and sequence similarity of FliI to F0F1, vacuolar, and archaebacterial ATPase subunits. J Bacteriol 173: 3564–3572. 37. Dreyfus G, Williams AW, Kawagishi I, Macnab RM (1993) Genetic and biochemical analysis of Salmonella typhimurium FliI, a flagellar protein related to the catalytic subunit of the F0F1 ATPase and to virulence proteins of mammalian and plant pathogens. J Bacteriol 175: 3131–3138. 38. Pallen MJ, Bailey CM, Beatson SA (2006) Evolutionary links between FliH/ YscL-like proteins from bacterial type III secretion systems and second-stalk components of the FoF1 and vacuolar ATPases. Protein Sci 15: 935–941. 39. Mulkidjanian AY, Makarova KS, Galperin MY, Koonin EV (2007) Inventing the dynamo machine: the evolution of the F-type and V-type ATPases. Nat Rev Microbiol 5: 892–899. 40. Venkatesan MM, Buysse JM, Oaks EV (1992) Surface presentation of Shigella flexneri invasion plasmid antigens requires the products of the spa locus. J Bacteriol 174: 1990–2001. 41. Woestyn S, Allaoui A, Wattiau P, Cornelis GR (1994) YscN, the putative energizer of the Yersinia Yop secretion machinery. J Bacteriol 176: 1561–1569. Origins and Diversification of T3SS 42. Eichelberg K, Ginocchio CC, Gala´n JE (1994) Molecular and functional characterization of the Salmonella typhimurium invasion genes invB and invC: homology of InvC to the F0F1 ATPase family of proteins. J Bacteriol 176: 4501–4510. 43. Galan JE (2008) Energizing type III secretion machines: what is the fuel? Nat Struct Mol Biol 15: 127–128. 44. Lara-Tejero M, Kato J, Wagner S, Liu X, Galan JE (2011) A sorting platform determines the order of protein secretion in bacterial type III systems. Science 331: 1188–1191. 45. Edqvist PJ, Olsson J, Lavander M, Sundberg L, Forsberg A, et al. (2003) YscP and YscU regulate substrate specificity of the Yersinia type III secretion system. J Bacteriol 185: 2259–2266. 46. Zarivach R, Deng W, Vuckovic M, Felise HB, Nguyen HV, et al. (2008) Structural analysis of the essential self-cleaving type III secretion proteins EscU and SpaS. Nature 453: 124–127. 47. Tamano K, Katayama E, Toyotome T, Sasakawa C (2002) Shigella Spa32 is an essential secretory protein for functional type III secretion machinery and uniformity of its needle length. J Bacteriol 184: 1244–1252. 48. Journet L, Agrain C, Broz P, Cornelis GR (2003) The needle length of bacterial injectisomes is determined by a molecular ruler. Science 302: 1757–1760. 49. Wood SE, Jin J, Lloyd SA (2008) YscP and YscU switch the substrate specificity of the Yersinia type III secretion system by regulating export of the inner rod protein YscI. J Bacteriol 190: 4252–4262. 50. Diepold A, Amstutz M, Abel S, Sorg I, Jenal U, et al. (2010) Deciphering the assembly of the Yersinia type III secretion injectisome. EMBO J 29: 1928– 1940. 51. Diepold A, Wiesand U, Cornelis GR (2011) The assembly of the export apparatus (YscR,S,T,U,V) of the Yersinia type III secretion apparatus occurs independently of other structural components and involves the formation of an YscV oligomer. Mol Microbiol 82: 502–514. 52. Wagner S, Konigsmaier L, Lara-Tejero M, Lefebre M, Marlovits TC, et al. (2010) Organization and coordinated assembly of the type III secretion export apparatus. Proc Natl Acad Sci U S A 107: 17745–17750. 53. Sukhan A, Kubori T, Wilson J, Galan JE (2001) Genetic analysis of assembly of the Salmonella enterica serovar Typhimurium type III secretion-associated needle complex. J Bacteriol 183: 1159–1167. 54. Deane JE, Abrusci P, Johnson S, Lea SM (2010) Timing is everything: the regulation of type III secretion. Cell Mol Life Sci 67: 1065–1075. 55. Blocker A, Komoriya K, Aizawa S (2003) Type III secretion systems and bacterial flagella: insights into their function from structural similarities. Proc Natl Acad Sci U S A 100: 3027–3030. 56. Ferris HU, Minamino T (2006) Flipping the switch: bringing order to flagellar assembly. Trends Microbiol 14: 519–526. 57. Minamino T, Namba K (2004) Self-assembly and type III protein export of the bacterial flagellum. J Mol Microbiol Biotechnol 7: 5–17. 58. Mota LJ, Journet L, Sorg I, Agrain C, Cornelis GR (2005) Bacterial injectisomes: needle length does matter. Science 307: 1278. 59. Kenjale R, Wilson J, Zenk SF, Saurya S, Picking WL, et al. (2005) The needle component of the type III secreton of Shigella regulates the activity of the secretion apparatus. J Biol Chem 280: 42929–42937. 60. Edgren T, Forsberg A, Rosqvist R, Wolf-Watz H (2012) Type III Secretion in Yersinia: Injectisome or Not? PLoS Pathog 8: e1002669. doi:10.1371/ journal.ppat.1002669 61. Pallen MJ, Beatson SA, Bailey CM (2005) Bioinformatics, genomics and evolution of non-flagellar type-III secretion systems: a Darwinian perspective. FEMS Microbiol Rev 29: 201–229. 62. Troisfontaines P, Cornelis GR (2005) Type III secretion: more systems than you think. Physiology 20: 326–339. 63. Blocker A, Gounon P, Larquet E, Niebuhr K, Cabiaux V, et al. (1999) The tripartite type III secreton of Shigella flexneri inserts IpaB and IpaC into host membranes. J Cell Biol 147: 683–693. 64. Shea JE, Hensel M, Gleeson C, Holden DW (1996) Identification of a virulence locus encoding a second type III secretion system in Salmonella typhimurium. Proc Natl Acad Sci U S A 93: 2593–2597. 65. Ochman H, Soncini FC, Solomon F, Groisman EA (1996) Identification of a pathogenicity island required for Salmonella survival in host cells. Proc Natl Acad Sci U S A 93: 7800–7804. 66. Cornelis GR, Wolf-Watz H (1997) The Yersinia Yop virulon: a bacterial system for subverting eukaryotic cells. Mol Microbiol 23: 861–867. 67. Peters J, Wilson DP, Myers G, Timms P, Bavoil PM (2007) Type III secretion a` la Chlamydia. Trends Microbiol 15: 241–251. 68. Rahme LG, Mindrinos MN, Panopoulos NJ (1991) Genetic and transcriptional organization of the hrp cluster of Pseudomonas syringae pv. phaseolicola. J Bacteriol 173: 575–586. 69. Van Gijsegem F, Gough C, Zischek C, Niqueux E, Arlat M, et al. (1995) The hrp gene locus of Pseudomonas solanacearum, which controls the production of a type III secretion system, encodes eight proteins related to components of the bacterial flagellar biogenesis complex. Mol Microbiol 15: 1095–1114. 70. Ginocchio CC, Olmsted SB, Wells CL, Galan JE (1994) Contact with epithelial cells induces the formation of surface appendages on Salmonella typhimurium. Cell 76: 717–724. 71. Pallen MJ, Matzke NJ (2006) From The Origin of Species to the origin of bacterial flagella. Nat Rev Microbiol 4: 784–790. PLOS Genetics | www.plosgenetics.org 13 September 2012 | Volume 8 | Issue 9 | e1002983