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  • Title: Rhizobium leguminosarum bv. trifolii PssP protein is required for exopolysaccharide biosynthesis and polymerization.
    Author: Mazur A, Król JE, Wielbo J, Urbanik-Sypniewska T, Skorupska A.
    Journal: Mol Plant Microbe Interact; 2002 Apr; 15(4):388-97. PubMed ID: 12026178.
    Abstract:
    Rhizobium leguminosarum bv. trifolii produces an acidic exopolysaccharide (EPS) that is important for the induction of nitrogen-fixing nodules on clover. Recently, three genes, pssN, pssO, and pssP, possibly involved in EPS biosynthesis and polymerization were identified. The predicted protein product of the pssP gene shows a significant sequence similarity to other proteins belonging to the PCP2a family that are involved in the synthesis of high-molecular-weight EPS. An R. leguminosarum bv. trifolii TA1 mutant with the entire coding region of pssP deleted did not produce the EPS. A pssP mutant with the 5' end of the gene disrupted produced exclusively low-molecular-weight EPS. A mutant that synthesized a functional N-terminal periplasmic domain but lacked the C-terminal part of PssP produced significantly reduced amounts of EPS with a slightly changed low to high molecular form ratio. Mutants affected in the PssP protein carrying a stable plasmid with a constitutively expressed gusA gene induced nodules on red clover that were not fully occupied by bacteria. A mutant with the entire pssP gene deleted infected only a few plant cells in the nodule. The pssP promoter-gusA reporter fusion was active in bacteroids during nodule development.
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