Yu Zhang1, Cheng-Xin Mao1, Xiao-Yu Zhai1, Pierce A Jamieson2, Chuan-Qing Zhang1. 1. Department of Crop Protection, Zhejiang Agriculture and Forest University, Hangzhou, China. 2. Department of Plant Pathology and Microbiology, and Institute for Plant Genomics and Biotechnology, Texas A&M University, College Station, TX, USA.
Abstract
BACKGROUND: Fusarium 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. It was found that 21.13% and 3.96% of the strains examined were highly resistant (HR) to prochloraz during 2017 to 2018. The HR strains contained a point mutation (S312T) in the FfCYP51B protein, while the strains identified with prochloraz susceptibility had no such point mutation in FfCYP51A/B/C. To confirm whether the mutations in FfCYP51B confer resistance to prochloraz, we exchanged the CYP51B locus between the sensitive strain and the resistant strain by homologous double exchange. The transformed mutants with a copy of the resistant fragment exhibited resistance to prochloraz, and the transformed mutants with a copy of the sensitive fragment exhibited sensitivity to prochloraz. Furthermore, 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 lead to the prochloraz-resistant phenotype in F. fujikuroi.
BACKGROUND:Fusarium 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. It was found that 21.13% and 3.96% of the strains examined were highly resistant (HR) to prochloraz during 2017 to 2018. The HR strains contained a point mutation (S312T) in the FfCYP51B protein, while the strains identified with prochloraz susceptibility had no such point mutation in FfCYP51A/B/C. To confirm whether the mutations in FfCYP51B confer resistance to prochloraz, we exchanged the CYP51B locus between the sensitive strain and the resistant strain by homologous double exchange. The transformed mutants with a copy of the resistant fragment exhibited resistance to prochloraz, and the transformed mutants with a copy of the sensitive fragment exhibited sensitivity to prochloraz. Furthermore, 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 lead to the prochloraz-resistant phenotype in F. fujikuroi.