Induction of Rhizobium meliloti nodC gene by Alnus incana compounds

An expression of nodC promoter of R. meliloti 1021, cloned in front of the Escherichia coli lacZ gene, was used to study the presence of R. meliloti nodC gene-inducing compound(s) in extracts and exudates of A. incana seeds and roots. The regulatory gene nodD was expressed at comparable level in bacterial culture of R. meliloti with and without the studied plant extracts and exudates, whereas the nodC-lacZ fusion expression was increased 4 times by seed exudates of grey alder and 2 times by seed extracts and root ingredients in comparison to the nodC-lacZ fusion expression in R. meliloti grown in a medium free of plant compounds. Induction of R. meliloti nodC gene expression by A. incana substances was also supported in plant test. Sterile filtrate of coculture of R. meliloti with seed exudates of A. incana induced root hair deformations and nodule-like structures on Medicago sativa.