Flavonoids induce temporal shifts in gene‐expression of nod‐box controlled loci in Rhizobium sp. NGR234

• Published in: Molecular microbiology Vol. 51; no. 2; pp. 335 - 347
• Main Authors: Kobayashi, Hajime, Graven, Yamama Naciri, Broughton, William J., Perret, Xavier
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Science Ltd 01.01.2004; Blackwell Science; Blackwell Publishing Ltd
• Subjects: Bacteriology; Base Sequence; Biological and medical sciences; Cloning, Molecular; DNA Primers; Escherichia coli - genetics; Flavonoids - pharmacology; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Bacterial - drug effects; Kinetics; Lipopolysaccharides - biosynthesis; Microbiology; Miscellaneous; Molecular Sequence Data; NodD protein; Polymerase Chain Reaction; Recombinant Proteins - metabolism; Rhizobium; Rhizobium - drug effects; Rhizobium - genetics; syrM gene; Bacteria; Rhizobium; Rhizobiaceae; Microbiology; Gene expression; Flavonoid
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1046/j.1365-2958.2003.03841.x

Summary Rhizobia, soil bacteria of the Rhizobiales, enter the roots of homologous legumes, where they induce the formation of nitrogen‐fixing nodules. Signals emanating from both symbiotic partners control nodule development. Efficient nodulation requires precise, temporal regulation of symbiotic genes. Roots continuously release flavonoids that interact with transcriptional activators of the LysR family. NodD proteins, which are members of this family, act both as sensors of the environment and modulate the expression of genes preceded by conserved promoter sequences called nod‐boxes. The symbiotic plasmid of the broad host‐range Rhizobium sp. NGR234 caries 19 nod‐boxes (NB1 to NB19), all of which were cloned upstream of a lacZ‐reporter gene. A flavonoid, daidzein was able to induce 18 of the 19 nod‐boxes in a NodD1‐dependent manner. Interestingly, induction of four nod‐boxes (NB6, NB15, NB16 and NB17) is highly dependent on NodD2 and was delayed  in  comparison  with  the  others.  In  turn, NodD2 is involved in the repression of the NB8 nodABCIJnolOnoeI operon. Activation of transcription of nodD2 is also dependent on flavonoids despite  the  absence  of  a  nod‐box  like  sequence  in the upstream promoter region. Mutational analysis showed that syrM 2 (another member of the LysR family), which is controlled by NB19, is also necessary for expression of nodD 2. Thus, NodD1, NodD2 and SyrM2 co‐modulate a flavonoid‐inducible regulatory cascade that coordinates the expression of symbiotic genes with nodule development.