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(NAS Colloquium) Virulence and Defense in Host--Pathogen Interactions Common Features Between Plants and Animals (2001) / Chapter Skim
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Pseudomonas syringae Hrp Type III Secretion System and Effector Proteins
Pages 19-26

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From page 19...
... A fundamental difference between this group of plant pathogens and most of the animal pathogens is that the former do not enter living host cells, but rather interact with the host cytoplasm from outside of an approximately 200-nm-thick plant cell wall. The ability to deliver effector proteins across this barrier via the type III secretion system is likely to be unique to plant pathogens, and it is key to their pathogenicity.
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From page 20...
... , such that enough individual plant cells undergo the HR to produce a confluent collapse. The DNA sequence of pHIR11 reveals a 25-kb cluster of hrp/hrc genes linked to an apparent operon encoding hopPsyA (`hrm~l)
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From page 21...
... The minimum genetic requirements for being a bacterial parasite of plants are unknown. Parasitism apparently requires the delivery of multiple effector proteins that suppress general antibacterial defenses and/or promote nutrient release from plant cells.
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From page 22...
... in culture, which complicates genetic dissection of the role of HrpA in the translocation of effector proteins into plant cells. Furthermore, no mutations in P
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From page 23...
... HrpK and CEL ORF1 The hrpL and hrpR genes bracket a cluster of operons that contain both hrp and hrc genes and appear sufficient to encode a complete Hrp type III secretion system. hrpK and the CEL ORF1 reside in the two borders between this core hrp/hrc cluster and known effecter genes, and the functions of these two genes are unknown.
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From page 24...
... These observations extend the original discovery of heterologous delivery of effecters by the type III secretion systems of Yersinia, Salmonella, and Shigella, and they strongly suggest the existence of universal targeting signals in proteins traveling all type III secretion pathways (69~. Yersinia secretes multiple Yops Yersinia outer proteins)
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From page 25...
... Thus, the requirements for HR elicitation can be reduced to two components: a functional Hrp type III secretion system and an injected effecter protein that is recognized by the it-gene surveillance system of the test plant. Hrp protein secretion in culture can be further dissected genetically, revealing two operons directing export across the inner membrane and another directing export across the outer membrane.
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From page 26...
... (1997) Pseudomonas syringae Pathovars and Related Pathogens (Kluwer, Dordrecht, The Netherlands)
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Key Terms

  • iii secretion
  • plant cells
  • effector proteins
  • hrp pai
  • avr proteins

  • effector protein
  • effector locus
  • targeting signal
  • plant pathogens
  • host cells

  • effector genes
  • syringae hrp
  • conserved effector
  • animal pathogens
  • hrp regulon

  • gene surveillance
  • universal targeting
  • host range
  • mrna targeting
  • genetic elements

  • exchangeable effector
  • mobile genetic
  • plant cell
  • host plants
  • encode effector

  • protein secretion
  • outer protein
  • syringae avr
  • avr genes
  • outer membrane


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