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Sinorhizobium fredii HH103 Mutants Affected in Capsular Polysaccharide (KPS) are Impaired for Nodulation with Soybean and Cajanus cajan

January 2006 , Volume 19 , Number  1
Pages  43 - 52

Maribel Parada , 1 José M. Vinardell , 1 Francisco J. Ollero , 1 ángeles Hidalgo , 1 Rocío Gutiérrez , 1 Ana M. Buendía-Clavería , 1 Wang Lei , 1 Isabel Margaret , 1 Francisco J. López-Baena , 1 Antonio M. Gil-Serrano , 2 Miguel A. Rodríguez-Carvajal , 2 Javier Moreno , 3 and José E. Ruiz-Sainz 1

1Departamento de Microbiología, Facultad de Biología, Universidad de Sevilla, Av. Reina Mercedes 6. 41012-Sevilla, Spain; 2Departamento de Química Orgánica, Facultad de Química, Universidad de Sevilla, Apdo. 553. 41071-Sevilla, Spain; 3Departamento de Biología Celular, Facultad de Biología, Universidad de Sevilla, Av. Reina Mercedes 6. 41012-Sevilla, Spain


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Accepted 7 September 2005.

The Sinorhizobium fredii HH103 rkp-1 region, which is involved in capsular polysaccharides (KPS) production, was isolated and sequenced. The organization of the S. fredii genes identified, rkpUAGHIJ and kpsF3, was identical to that described for S. meliloti 1021 but different from that of S. meliloti AK631. The long rkpA gene (7.5 kb) of S. fredii HH103 and S. meliloti 1021 appears as a fusion of six clustered AK631 genes, rkpABCDEF. S. fredii HH103-Rifr mutants affected in rkpH or rkpG were constructed. An exoA mutant unable to produce exopolysaccharide (EPS) and a double mutant exoA rkpH also were obtained. Glycine max (soybean) and Cajanus cajan (pigeon pea) plants inoculated with the rkpH, rkpG, and rkpH exoA derivatives of S. fredii HH103 showed reduced nodulation and severe symptoms of nitrogen starvation. The symbiotic capacity of the exoA mutant was not significantly altered. All these results indicate that KPS, but not EPS, is of crucial importance for the symbiotic capacity of S. fredii HH103-Rifr. S. meliloti strains that produce only EPS or KPS are still effective with alfalfa. In S. fredii HH103, however, EPS and KPS are not equivalent, because mutants in rkp genes are symbiotically impaired regardless of whether or not EPS is produced.



© 2006 The American Phytopathological Society