ABSTRACT
The nodFEL and nodMNT operons in Rhizobium leguminosarum biovar viciae are transcribed in the same orientation and induced by NodD in response to flavonoids secreted by legumes. In the narrow intergenic region between nodFEL and nodMNT, we identified a small gene divergently transcribed from nodM to the 3' end of nodL. Unlike the promoters upstream of nodF and nodM, the promoter of this gene is constitutively expressed. It appeared that its promoter might partially overlap with that of nodM and its expression was repressed by nodD. A deletion mutation was made and proteins produced by the mutant were compared with those by wild-type using 2D gel electrophoresis. Several protein differences were identified suggesting that this small gene influences the expression or stability of these proteins. However, the mutant nodulated its host plant (pea) normally.
Subject(s)
Bacterial Proteins/metabolism , Glutamine-Fructose-6-Phosphate Transaminase (Isomerizing)/metabolism , Operon , Rhizobium leguminosarum/metabolism , Bacterial Proteins/genetics , Electrophoresis, Gel, Two-Dimensional , Fabaceae/metabolism , Fabaceae/microbiology , Flavonoids/metabolism , Flavonoids/pharmacology , Gene Expression Regulation, Bacterial/drug effects , Genetic Variation , Glutamine-Fructose-6-Phosphate Transaminase (Isomerizing)/genetics , Host-Pathogen Interactions , Mutation , Promoter Regions, Genetic/genetics , Reverse Transcriptase Polymerase Chain Reaction , Rhizobium leguminosarum/genetics , Rhizobium leguminosarum/physiology , Root Nodules, Plant/metabolism , Root Nodules, Plant/microbiologyABSTRACT
In Rhizobium leguminosarum bv. viciae, NodD, as a member of the LysR-type transcriptional regulators (LTTRs), exerts auto-regulation and activates transcription of other nod genes in the presence of naringenin. LTTRs were typically composed of N-terminal DNA-binding domain and C-terminal regulatory domain. In this study, by systematic insertion mutation, a region of 12 amino acids in length of NodD was identified as functional domain. Insertion mutants in this region appeared to acquire the ability of constitutively activating nodA gene and retained their auto-regulation properties. This identified region was shown to be a hinge of NodD as revealed through the model built using Swiss- PDB Viewer software. It is the first time to report that as a member of LysR family, NodD has been shown to contain a short intramolecular domain that influences its performance.
