RpoN (σ54) is required for plasmid-encoded coronatine biosynthesis in Pseudomonas syringae

Francisco J. Alarcón-Chaidez, Lisa Keith, Youfu Zhao, Carol L. Bender

Research output: Contribution to journalArticlepeer-review


The plant pathogen Pseudomonas syringae pv. glycinea PG4180 produces coronatine (COR), a phytotoxin which functions as a virulence factor in bacterial blight of soybeans. The COR biosynthetic gene cluster in PG4180 is borne on a 90-kb plasmid named p4180A. Although pathway-specific regulatory genes for COR have been identified, global regulatory genes for COR production in PG4180 remain undefined. In the present study, we evaluated the role of rpoN, which encodes σ54, in the virulence of strain PG4180. A rpoN mutant of PG4180, designated PG4180.K2, was unable to grow in M9 minimal medium; however, the addition of exogenous glutamate, glutamine or aspartate to M9 medium enabled PG4180.K2 to grow in vitro. PG4180.K2 could not induce disease symptoms or multiply in soybean plants and was defective in COR production and cor gene expression. Furthermore, PG4180.K2 was impaired in transcription of hrpL, an alternate σ factor that mediates expression of genes in the type III secretion system of P. syringae. PG4180.K2 transconjugants with a wild-type copy of rpoN were complemented for hrpL and cor gene expression, COR biosynthesis, and growth in vitro. Our results indicate that rpoN is required for growth and the expression of both chromosomal and plasmid-encoded virulence factors in P. syringae pv. glycinea PG4180.

Original languageEnglish (US)
Pages (from-to)106-117
Number of pages12
Issue number2
StatePublished - Mar 2003
Externally publishedYes


  • Hypersensitive response
  • Phytotoxin
  • Sigma factor
  • hrpL

ASJC Scopus subject areas

  • Molecular Biology


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