Browsing by Author "Metzler, Mary C."

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    The cellulase encoded by the native plasmid of Clavibacter michiganensis ssp. sepedonicus plays a role in virulence and contains an expansin-like domain. Physiol Mol Plant P
    (2000-10) Laine, Marko J.; Haapalainen, Minna; Wahlroos, Tony; KANKARE, Katja; Nissinen, Riitta; Kassuwi, shaaban A. A.; Metzler, Mary C.
    We are examining the molecular basis of pathogenicity for Clavibacter michiganensis ssp.sepedonicus , a gram positive coryneform bacterium that causes the economically important potato ring rot disease. We present here a complete restriction map of the native plasmid pCS1, on which we localize the cellulase gene that it contains. A mutant produced by chemical mutagenesis that does not produce cellulase as well as a naturally occurring strain that does not contain the pCS1 plasmid were both shown to be markedly reduced in virulence on eggplant. Both strains became significantly more virulent after the cellulase gene was introduced into the cells by transformation. The complete nucleotide sequence of the cellulase gene was determined and shown to encode a protein of 727 amino acids which would have a predicted molecular weight of 71.5 kDa. The sequence shows a leader sequence for secretion and two typical cellulase domains (a catalytic domain and a cellulose binding domain). Additionally, we identify an unexpected third domain that shows similarity to a plant protein called expansin, which is believed to interact with cellulose microfibrils during plant cell expansion.
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    In Planta - Complementation of Clavibacter Michiganensis Subsp. sepedonicus Strains Deficient in Cellulase Production or HR Induction Restores Virulence
    (2001-01) Nissinen, Riitta; Kassuwi, shaaban A. A.; Peltola, Riikka; Metzler, Mary C.
    Clavibacter michiganensis subsp. sepedonicus, a Gram positive bacterium that causes bacterial ring rot of potato, was studied in eggplant, an alternate host, using strains that differed in phenotype. Two factors affecting virulence, the ability to induce a hypersensitive response (HR) and cellulase production, were studied. A plasmid-free isolate of C. michiganensis subsp. sepedonicus that causes HR on tobacco but is unable to produce cellulase multiplied efficiently in planta, but caused only weak symptoms. In contrast, a strain that is unable to induce HR on tobacco but produces cellulase was impaired in the ability to multiply in the host and caused no symptoms. When the two non-virulent strains were coinoculated into eggplants, typical disease symptoms developed. This enhancement was not due to formation of a new phenotype or significant increases in population density of either of the strains. Our results suggest that both cellulase production and the ability to induce HR are required for a successful infection process and disease induction by C. michiganensis subsp. sepedonicus. Our results additionally suggest that the ability to induce HR on non-host plants is required for multiplication in the host plant, whereas cellulase expression is necessary for induction of disease symptoms.