Type III secretion system effector proteins: Double agents in bacterial disease and plant defense

James R. Alfano, Alan Collmer

Research output: Contribution to journalReview articlepeer-review

609 Scopus citations


Many phytopathogenic bacteria inject virulence effector proteins into plant cells via a Hrp type III secretion system (TTSS). Without the TTSS, these pathogens cannot defeat basal defenses, grow in plants, produce disease lesions in hosts, or elicit the hypersensitive response (HR) in nonhosts. Pathogen genome projects employing bioinformatic methods to identify TTSS Hrp regulon promoters and TTSS pathway targeting signals suggest that phytopathogenic Pseudomonas, Xanthomonas, and Rahtonia spp. harbor large arsenals of effectors. The Hrp TTSS employs customized cytoplasmic chaperones, conserved export components in the bacterial envelope (also used by the TTSS of animal pathogens), and a more specialized set of TTSS-secreted proteins to deliver effectors across the plant cell wall and plasma membrane. Many effectors can act as molecular double agents that betray the pathogen to plant defenses in some interactions and suppress host defenses in others. Investigations of the functions of effectors within plant cells have demonstrated the plasma membrane and nucleus as subcellular sites for several effectors, revealed some effectors to possess cysteine protease or protein tyrosine phosphatase activity, and provided new clues to the coevolution of bacterium-plant interactions.

Original languageEnglish (US)
Pages (from-to)385-414
Number of pages30
JournalAnnual Review of Phytopathology
StatePublished - 2004
Externally publishedYes


  • Avirulence genes
  • Hop proteins
  • Hypersensitive response
  • Plant disease
  • hrp genes

ASJC Scopus subject areas

  • Plant Science


Dive into the research topics of 'Type III secretion system effector proteins: Double agents in bacterial disease and plant defense'. Together they form a unique fingerprint.

Cite this