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Genetic Analysis of the rkp-3 Gene Region in Sinorhizobium meliloti 41: rkpY Directs Capsular Polysaccharide Synthesis to KR5 Antigen Production

November 2009 , Volume 22 , Number  11
Pages  1,422 - 1,430

Adrienn Pálvölgyi,1 Veronika Deák,1 Véréna Poinsot,2 Tibor Nagy,1 Enik Nagy,3 Ildikó Kerepesi,1 and Péter Putnoky1

1Department of Genetics and Molecular Biology, University of Pécs, P.O. Box 266, H-7604 Pécs, Hungary; 2Laboratoire des IMRCP, Université Paul Sabatier, F-31062 Toulouse, France; 3Institute of Genetics, Biological Research Center, Hungarian Academy of Sciences, P.O. Box 521, H-6701 Szeged, Hungary

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Accepted 17 June 2009.

Rhizobial surface polysaccharides, including capsular polysaccharides (KPS), are involved in symbiotic infection. The rkp-3 locus of Sinorhizobium meliloti 41 is responsible for the production of pseudaminic acid, one of the components of the KR5 antigen, a strain-specific KPS. We have extended the sequence determination and genetic dissection of the rkp-3 region to clarify the structure and function of the rkpY gene and to identify additional rkp genes. Except for rkpY, no other genes were found where mutation affected the KPS structure and symbiosis. These mutants show a unique phenotype producing a low molecular weight polysaccharide (LMW PS). Creating double mutants, we have shown that biosynthesis genes of the KR5 antigen except rkpZ are not necessary for the production of this LMW PS. Polysaccharide analysis of genetically modified strains suggests that rkpY has pleiotropic effects on polysaccharide production. It directs KPS synthesis to the KR5 antigen and influences lipo-oligo 3-deoxy-d-manno-2 octulosonic acid (Kdo) production in S. meliloti 41. In addition, rkpY suppresses the lipo-oligoKdo production when it is introduced into S. meliloti 1021.

© 2009 The American Phytopathological Society