E422A Point Mutation in the Myosin-5 Protein Confers Resistance to Phenamacril in Fusarium fujikuroi Field Isolates.

Rice bakanae disease, mainly caused by Fusarium fujikuroi, threatens rice production globally. Phenamacril is a site-targeted fungicide that inhibits myosin-5 in F. fujikuroi. Previous studies reported F. fujikuroi isolates resistant to phenamacril due to mutations at amino acid positions 218 and 219 of Ffmyosin-5. This study identified resistant isolates exhibiting a resistance factor of 97.15-173.84. However, these isolates carried no reported mutation sites in Ffmyosin-5. Resistant isolates exhibited reduced fitness and no cross-resistance to other commonly used fungicides. Sequence alignment showed that these resistant isolates contained the E422A mutation in the Ffmyosin-5 protein. Molecular docking revealed diminished binding affinity due to this mutation. The reduced sensitivity to phenamacril of F. fujikuroi transformants carrying the E422A mutation further confirmed the importance of this point mutation in fungicide resistance. A rapid AS-PCR method was developed for E422A detection. Collectively, this study identified E422A as a novel phenamacril-resistant mutation site and detailed the resistance mechanism in F. fujikuroi.