Mutation in cyp51b and overexpression of cyp51a and cyp51b confer multiple resistant to DMIs fungicide prochloraz in Fusarium fujikuroi.

BACKGROUND F. fujikuroi is a plant pathogen that causes rice bakanae disease. Prochloraz is an imidazole-class sterol 14α-demethylase inhibitor (DMI), which has been in use for several years as a foliar spray to control Fusarium spp. on agriculturally important monocot crops. F. fujikuroi is highly resistant to prochloraz treatment, and the aim of this study was to clarify the mechanism by which F. fujikuroi renders itself resistant to prochloraz. RESULTS Recently, prochloraz-resistant strains were identified over a vast geographical area in the agricultural regions of Zhejiang Province, China. 21.13% and 3.96% of the strains examined were highly resistant (HR) to prochloraz during 2017 to 2018. The HR strains were found to contain a point mutation (S312T) in the FfCYP51B protein, while the strains identified with prochloraz susceptibility had no such point mutation in FfCYP51A/B/C. Heterologous expression of Ffcyp51b from prochloraz resistant strains in sensitive strain confirmed that the point mutation in Ffcyp51b produces the observed resistance of F. fujikuroi to prochloraz. Further, qRT-PCR analysis of Ffcyp51a/b/c gene expression revealed that Ffcyp51a and Ffcyp51b were significantly up-regulated in the prochloraz-resistant strains relative to the sensitive strains in F. fujikuroi. Contrary to our expectation, docking of prochloraz into the modeled binding pocket of FfCYP51B indicated that the affinity between prochloraz and the FfCYP51B increased after the amino acid at codon 312 changed to Thr. CONCLUSION The point mutation S312T in FfCYP51B and overexpression of Ffcyp51a and Ffcyp51b together leads to the prochloraz resistant phenotype in F. fujikuroi. This article is protected by copyright. All rights reserved.