Overexpression of the 14α-Demethylase Target Gene (CYP51) Mediates Fungicide Resistance in Blumeriella jaapii

Sterol demethylation inhibitor (DMI) fungicides are widely used to control fungi pathogenic to humans and plants. Resistance to DMIs is mediated either through alterations in the structure of the target enzyme CYP51 (encoding 14α-demethylase), through increased expression of the CYP51 gene, or through increased expression of efflux pumps. We found that CYP51 expression in DMI-resistant (DMI^R) isolates of the cherry leaf spot pathogen Blumeriella jaapii was increased 5- to 12-fold compared to that in DMI-sensitive (DMI^S) isolates. Analysis of sequences upstream of CYP51 in 59 DMI^R isolates revealed that various forms of a truncated non-long terminal direct repeat long interspersed nuclear element retrotransposon were present in all instances. Similar inserts upstream of CYP51 were not present in any of 22 DMI^S isolates examined.