title: C239S Mutation in the β-Tubulin of Phytophthora sojae Confers Resistance to Zoxamide.
abstract: Zoxamide is the sole β-tubulin inhibitor registered for the control of oomycete pathogens. The current study investigated the activity of zoxamide against Phytophthora sojae and baseline sensitivity was established with a mean EC50 of 0.048 μg/ml. The data is critical for monitoring changes in zoxamide-sensitivity in the field. Three stable resistant mutants with a high resistance level were obtained by selection on zoxamide amended media. Although the development of resistance occurred at a low frequency, there were no apparent fitness penalty in the acquired mutants in terms of growth rate, sporulation, germination and pathogenicity. Based on the biological profiles and low mutagenesis rate, the resistance risk of P. sojae to zoxamide can be estimated as low to medium. Further investigation revealed all the zoxamide-resistant mutants had a point mutation of C239S in their β-tubulin. Zoxamide also exhibited high activity against most species from the genus Pythium in which only Pythium aphanidermatum was found naturally resistant to zoxamide and harboring the natural point mutation S239 in the β-tubulin. Back-transformation in P. sojae with the mutated allele (S239) confirmed the C239S mutation can induce resistance to zoxamide, and the resistance level was positively related to the expression level of the mutated gene. In contrast, the overexpression of the wild type gene was unable to cause zoxamide resistance. It is the first report on the resistance molecular mechanism of zoxamide in oomycetes. Based on our study, C239 is supposed to be a key target site of zoxamide, which distinguishes zoxamide from benzimidazoles and accounts for its low resistance risk. The result can provide advice on the design of new β-tubulin inhibitors in future.
authors.affiliation: Department of Plant Pathology, China Agricultural UniversityBeijing, China; Department of Botany and Plant Pathology, Oregon State University, CorvallisOR, USA.
authors.forename: Meng
authors.initials: M
authors.lastname: Cai
authors.affiliation: Department of Plant Pathology, China Agricultural University Beijing, China.
authors.forename: Jianqiang
authors.initials: J
authors.lastname: Miao
authors.affiliation: Department of Plant Pathology, China Agricultural University Beijing, China.
authors.forename: Xi
authors.initials: X
authors.lastname: Song
authors.affiliation: Department of Plant Pathology, China Agricultural University Beijing, China.
authors.forename: Dong
authors.initials: D
authors.lastname: Lin
authors.affiliation: Plant Science and Technology College, Beijing University of Agriculture Beijing, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Bi
authors.affiliation: College of Forestry, Beijing Forestry University Beijing, China.
authors.forename: Lei
authors.initials: L
authors.lastname: Chen
authors.affiliation: Department of Plant Pathology, China Agricultural University Beijing, China.
authors.forename: Xili
authors.initials: X
authors.lastname: Liu
authors.affiliation: Department of Botany and Plant Pathology, Oregon State University, Corvallis OR, USA.
authors.forename: Brett M
authors.initials: BM
authors.lastname: Tyler
keywords: C239S; molecular mechanism of resistance; oomycetes; resistance risk; zoxamide; β-tubulin inhibitor