Rhizobia are bacterial symbionts of plants in the genus Phaseolus. The formation of this symbiosis is dependent upon specific chemical signals produced by both the host plant and the soil bacteria and culminates in the formation of a new plant organ, the root nodule. Plant nodulation (nod) genes encoding flavonoids initiate nodulation by inducing transcription of bacterial genes. The bacterial genes produce lipo-chitin oligosaccharide (LCO) signal molecules or nod factors. These nod factors in turn signal the host root cells to divide and multiply. LCOs not only play a role in the initiation of nodule formation but also play a major part in the bacterial specificity. Many nod factors have been isolated and all of them have a similar backbone made of 3 to 5 b-1,4-linked N- acetyl glucosamine residues linked to a fatty acyl chain. LCO structure differs only in their modifications and these modifications are believed to determine host specificity for the bacteria. Bacteria that nodulate the common bean Phaseolus vulgaris are all in the genus Rhizobium. Because they have the same host range, they are believed to have LCOs with similar modifications. My lab has isolated a mutant P. vulgaris with the ability to restrict nodulation of all bacteria in the genus Rhizobium except for three strains. This experiment was developed in order to determine if the LCOs produced by these three strains differ from other strains within the genus. LCO production was induced by addition of the plant flavonoid naringenin and the LCOs were isolated using reversed-phase high-performance liquid chromatography (HPLC). The bacterial genes that encode these specific LCO structures will be isolated and sequenced.

Key words: lipo-chitin oligosaccharides, nod factors, nodulation, Phaseolus vulgaris, rhizobia