NopC Is a Rhizobium-Specific Type 3 Secretion System Effector Secreted by Sinorhizobium (Ensifer) fredii HH103

• Published in: PloS one 2015-11, Vol.10 (11), p.e0142866
• Main Authors: Jiménez-Guerrero, Irene, Pérez-Montaño, Francisco, Medina, Carlos, Ollero, Francisco Javier, López-Baena, Francisco Javier
• Format: Article
• Language: English
• Subjects: Adenylate cyclase; Bacteria; Bacterial Proteins - metabolism; Cellular signal transduction; Cloning; Cytoplasm - metabolism; E coli; Escherichia coli; Flavonoids; Flavonoids - pharmacology; Gene Deletion; Gene expression; Gene Expression Regulation, Bacterial - drug effects; Genes; Genetic Loci; Glycine max; Glycine max - microbiology; Health aspects; Homology; In vivo methods and tests; Infections; Kinases; Legumes; Nitrogen fixation; Nodulation; Nodules; Plant Root Nodulation - drug effects; Plant Roots - cytology; Plant Roots - microbiology; Plasmids; Protein Transport - drug effects; Proteins; Secretion; Signal transduction; Sinorhizobium - drug effects; Sinorhizobium - metabolism; Soybeans; Species Specificity; Symbiosis; Transduction; Type III Secretion Systems - metabolism; Vigna unguiculata; Virulence
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0142866

Sinorhizobium (Ensifer) fredii HH103 is a broad host-range nitrogen-fixing bacterium able to nodulate many legumes, including soybean. In several rhizobia, root nodulation is influenced by proteins secreted through the type 3 secretion system (T3SS). This specialized secretion apparatus is a common virulence mechanism of many plant and animal pathogenic bacteria that delivers proteins, called effectors, directly into the eukaryotic host cells where they interfere with signal transduction pathways and promote infection by suppressing host defenses. In rhizobia, secreted proteins, called nodulation outer proteins (Nops), are involved in host-range determination and symbiotic efficiency. S. fredii HH103 secretes at least eight Nops through the T3SS. Interestingly, there are Rhizobium-specific Nops, such as NopC, which do not have homologues in pathogenic bacteria. In this work we studied the S. fredii HH103 nopC gene and confirmed that its expression was regulated in a flavonoid-, NodD1- and TtsI-dependent manner. Besides, in vivo bioluminescent studies indicated that the S. fredii HH103 T3SS was expressed in young soybean nodules and adenylate cyclase assays confirmed that NopC was delivered directly into soybean root cells by means of the T3SS machinery. Finally, nodulation assays showed that NopC exerted a positive effect on symbiosis with Glycine max cv. Williams 82 and Vigna unguiculata. All these results indicate that NopC can be considered a Rhizobium-specific effector secreted by S. fredii HH103.