A Conservative Mutant Version of the Mrr1 Transcription Factor Correlates with Reduced Sensitivity to Fludioxonil in .

Fludioxonil is a highly effective phenylpyrrole fungicide for controlling . Although the field efficacy of fludioxonil remains high, isolates with reduced sensitivity have been reported globally. The molecular target of fludioxonil still remains unknown; however, a mechanism of reduced sensitivity to fludioxonil underlies the overexpression of the ATP binding cassette (ABC) transporter AtrB in a dependent pathway of the Mrr1 transcription factor. Fludioxonil is a key player in controlling infection in table grapes in Chile. However, some isolates with a reduced sensitivity to fludioxonil were detected. This study observed endogenous overexpression in Chilean isolates with reduced sensitivity to fludioxonil ( = 22) compared to the sensitive isolates ( = 10). All isolates increased the expression of in a growth medium supplemented with fludioxonil (0.05 μg/mL). However, sensitive isolates showed lower expression than those with reduced fludioxonil sensitivity. Remarkably, a mutant version of the transcription factor Mrr1 carrying 21 amino acid modifications was identified in all isolates with reduced sensitivity to fludioxonil. These changes alter the protein's transcription factor domain and the C-terminal portion of the protein but not the Zn (2)-C6 fungal-type DNA-binding domain. These results suggest a direct relationship between the conserved and divergent mutant version of and sensitivity to fludioxonil. This study provides a new target for developing molecular diagnostic strategies to monitor 's sensitivity to fludioxonil in the field.