Identification of Sinorhizobium meliloti genes regulated during symbiosis

RNA fingerprinting by arbitrarily primed PCR was used to isolate Sinorhizob ium meliloti genes regulated during the symbiotic interaction with alfalfa (Medicago sativa), Sixteen partial cDNAs were isolated whose corresponding genes were differentially expressed between symbiotic and free-living condi tions. Thirteen sequences corresponded to genes up-regulated during symbios is, whereas three were instead repressed during establishment of the symbio tic interaction. Seven cDNAs corresponded to known or predicted nif and fix genes. Four presented high sequence similarity with genes not yet identifi ed in S, meliloti, including genes encoding a component of the pyruvate deh ydrogenase complex, a cell surface protein component, a copper transporter, and an argininosuccinate lyase, Finally, five cDNAs did not exhibit any si milarity with sequences present in databases, A detailed expression analysi s of the nine non-nif-fix genes provided evidence for an unexpected variety of regulatory patterns, most of which have not been described so far.