Moon-Sik Yang,2 and
1Division of Natural Sciences and Technology, Wonkwang University, Iksan, Chonbuk 570-749, Korea; 2Institute for Molecular Biology and Genetics, Research Center of Bioactive Materials, Chonbuk National University, Jeonju, Chonbuk 561-756, Korea; 3Department of Agricultural Biology, Chungbuk National University, Cheongju, Chungbuk 361-763, Korea
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Accepted 12 August 2008.
A new laccase gene (lac3) from the chestnut blight fungus Cryphonectria parasitica was induced by the presence of tannic acid, which is abundant in the bark of chestnut trees and is assumed to be one of the major barriers against pathogen infection. However, other commonly known laccase inducers, including ferulic acid, 2,5-xylidine, catechol, and pH, did not induce lac3 transcription. Moreover, the hypovirus modulated the induction of lac3 transcription, abolishing the transcriptional induction of the lac3 gene by tannic acid. A functional analysis of lac3 using a lac3-null mutant indicated that fungal growth and other morphological characteristics, including pigmentation and sporulation, were not affected. However, a virulence assay indicated that the loss of function of a tannic acid--inducible and hypoviral-regulated laccase resulted in reduced virulence without detectable changes in the morphological features. The constitutive expression of lac3 resulted in no significant differences in the necrotic lesions from those caused by the wild type, but its expression in the presence of the hypovirus led to larger lesions than those caused by the hypovirulent strain. These results suggest that the lac3 gene product may not be the only determinant of fungal virulence in chestnut trees but is an important factor.
© 2008 The American Phytopathological Society