Imazalil resistance linked to a unique insertion sequence in the PdCYP51 promoter region of Penicillium digitatum
2007
Ghosoph, J.M. | Schmidt, L.S. | Margosan, D.A. | Smilanick, J.L.
Two mechanisms of resistance to the fungicide imazalil (IMZ) existed among California strains of Penicillium digitatum, cause of citrus green mold. Sensitive (S; n = 50) strains did not grow on IMZ above 0.1 μg mL-1, while those resistant (R; n = 59) grew >or=0.5 mg L-1. After amplification of the promoter region of the CYP51 gene, fragments 250, 450, and 750 bp in size were generated. All S strains had a 250 bp product, while among R strains, 47 had a 450 bp product and 12 had a 750 bp product. The 450 bp unit was common among R strains, while the 750 bp unit, reported previously by others, was not. The promoter region of all was identical; variations occurred in the region's transcriptional enhancer unit. S strains with a 250 bp product and R strains with a 750 bp product had one and five copies, respectively, of a 126 bp transcriptional enhancer unit. R strains with a 450 bp product had a unique 199 bp insert within the 126 bp transcriptional enhancer unit with no known sequence correlations (GenBank). Both types of R strains exhibited significantly elevated expression, approximately 10-fold, of the target site CYP51 gene, indicating its overexpression was the mechanism of resistance.
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