NopA is associated with cell surface appendages produced by the type III secretion system of Rhizobium sp. strain NGR234

William J. Deakin, Corinne Marie, Maged Saad, Hari B. Krishnan, William J. Broughton*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

45 Scopus citations


Rhizobium sp. strain NGR234, which is capable of interacting with a large number of legumes, utilizes a variety of signaling molecules to establish nitrogen-fixing symbioses. Among these are nodulation outer proteins (Nops) that transit through a type III secretion system (TTSS). Abolition of Nop secretion affects nodulation of certain legumes. Under free-living conditions, the secretion of Nops can be induced by the addition of flavonoids. Here, we show that an in-frame deletion of nopA abolishes secretion of all other Nops and has the same impact on nodule formation as mutations that lead to a nonfunctional TTSS. This secretion-minus phenotype of the nopA mutant, as well as bioinformatics analysis of NopA itself, suggests that NopA could be an external component of the TTSS. Electron microscopy showed that NGR234 synthesizes fibrillar structures on the cell surface in a flavonoid-inducible and NopA-dependent manner. Purification of the macromolecular surface appendages revealed that NopA is a major component of these structures.

Original languageEnglish (US)
Pages (from-to)499-507
Number of pages9
JournalMolecular Plant-Microbe Interactions
Issue number5
StatePublished - May 1 2005


  • Effector
  • Pathogenicity
  • Pilus
  • Translocator

ASJC Scopus subject areas

  • Physiology
  • Agronomy and Crop Science

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