Tandem repeat of a transcriptional enhancer upstream of the sterol 14 alpha-demethylase gene (CYP51) in Penicillium digitatum

We investigated the mechanism of resistance to demethylation inhibitors (DM I) in Penicillium digitatum by isolating the CYP51 gene, which encodes the target enzyme (P450(14DM)) of DMI, from three DMI-resistant and three DMI-s ensitive strains. The structural genes of all six strains were identical, b ut in the promoter region, a unique 126-bp sequence was tandemly repeated f ive times in the DMI-resistant strains and was present only once in the DMI -sensitive strains. Constitutive expression of CYP51 in the resistant strai ns was about 100-fold higher than that in the sensitive strains. We introdu ced CYP51, including the promoter region, from a DMI-resistant strain into a DMI-sensitive strain, which rendered the: transformants DMI resistant and increased CYP51 expression. We also found that if the number of copies of the repeat was reduced to two, resistance and CYP51 expression also decreas ed, These results indicate that the 126-bp unit acts as a transcriptional e nhancer and that a tandem repeat of the unit enhances CYP51 expression, res ulting in DR;II resistance. This is a new fungicide resistance mechanism fo r filamentous fungi.