Structural and functional analysis of the type III secretion system from Pseudomonas fluorescens Q8r1-96

Dmitri V. Mavrodi, Anna Joe, Olga V. Mavrodi, Karl A. Hassan, David M. Weller, Ian T. Paulsen, Joyce E. Loper, James R. Alfano, Linda S. Thomashow

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33 Scopus citations


Pseudomonas fluorescens Q8r1-96 represents a group of rhizosphere strains responsible for the suppressiveness of agricultural soils to take-all disease of wheat. It produces the antibiotic 2,4-diacetylphloroglucinol and aggressively colonizes the roots of cereal crops. In this study, we analyzed the genome of Q8r1-96 and identified a type III protein secretion system (T3SS) gene cluster that has overall organization similar to that of the T3SS gene cluster of the plant pathogen Pseudomonas syringae. We also screened a collection of 30 closely related P. fluorescens strains and detected the T3SS genes in all but one of them. The Q8r1-96 genome contained ropAA and ropM type III effector genes, which are orthologs of the P. syringae effector genes hopAA1-1 and hopM1, as well as a novel type III effector gene designated ropB. These type III effector genes encoded proteins that were secreted in culture and injected into plant cells by both P. syringae and Q8r1-96 T3SSs. The Q8r1-96 T3SS was expressed in the rhizosphere, but mutants lacking a functional T3SS were not altered in their rhizosphere competence. The Q8r1-96 type III effectors RopAA, RopB, and RopM were capable of suppressing the hypersensitive response and production of reactive oxygen species, two plant immune responses.

Original languageEnglish (US)
Pages (from-to)177-189
Number of pages13
JournalJournal of bacteriology
Issue number1
Publication statusPublished - Jan 1 2011


ASJC Scopus subject areas

  • Microbiology
  • Molecular Biology

Cite this

Mavrodi, D. V., Joe, A., Mavrodi, O. V., Hassan, K. A., Weller, D. M., Paulsen, I. T., ... Thomashow, L. S. (2011). Structural and functional analysis of the type III secretion system from Pseudomonas fluorescens Q8r1-96. Journal of bacteriology, 193(1), 177-189.