Molecular Analysis of the Laccase Gene from the Chestnut Blight Fungus and Selective Suppression of Its Expression in an Isogenic Hypovirulent Strain. Gil H. Choi. Department of Molecular Oncology and Virology, Roche Institute of Molecular Biology, Roche Research Center, Nutley, NJ 07110. Thomas G. Larson, and Donald L. Nuss. Department of Molecular Oncology and Virology, Roche Institute of Molecular Biology, Roche Research Center, Nutley, NJ 07110.. MPMI 5:119-128. Accepted 5 November 1991. Copyright 1992 The American Phytopathological Society.

The gene encoding laccase in the chestnut blight fungus, Cryphonectria parasitica, has been cloned and characterized. The predicted C. parasitica laccase amino acid sequence (591 aa) was 57% identical to the Neurospora crassa laccase sequence and contained four potential copper-binding regions that are conserved in a number of copper-binding proteins. Treatment of a virulent C. parasitica strain with 3 μM cycloheximide resulted in a marked increase in laccase mRNA accumulation, whereas identical treatment of an isogenic strain that contained a hypovirulence-associated virus failed to significantly increase laccase mRNA levels. In contrast, the accumulation of mRNAs encoding Beta-tubulin, actin, or glyceraldehyde-3-phosphate dehydrogenase was not appreciably altered by either the presence of a hypovirulence-associated virus or treatment with cycloheximide. These results provide evidence that the expression of a specific fungal gene encoding a known protein product is selectively modulated by a hypovirulence-associated virus.