College of Plant Protection, Nanjing Agricultural University, Nanjing 210095, PR China.
Phytopathology. 2009 Dec;99(12):1403-11. doi: 10.1094/PHYTO-99-12-1403.
ABSTRACT Wheat head blight caused by Gibberella zeae (anamorph: Fusarium graminearum) is a threat to food safety in China because of mycotoxin contamination of the harvested grain, the frequent occurrence of the disease, and the failure of chemical control in some areas due to benzimidazole resistance in the pathogen population. The molecular resistance mechanism, however, of G. zeae to benzimidazole fungicides (especially carbendazim; active ingredient: methyl benzimidazol-2-yl carbamate [MBC]) is poorly understood. DNA sequences of a beta-tubulin gene (beta(2)tub) (GenBank access number FG06611.1) in G. zeae were analyzed. Mutations in beta(2)tub in moderately resistant strains (MBC(MR)) included TTT (Phe)-->TAT (Tyr) at codon 167 or TTC (Phe)-->TAC (Tyr) at codon 200. A highly resistant strain (MBC(HR)) had two point mutations, one at codon 73, CAG (Gln)-->CGG (Arg), and the other at codon 198, GAG (Glu)-->CTG (Leu). To confirm that mutations in the beta(2)tub confer resistance to benzimidazole fungicides, the entire beta(2)tub locus was deleted from MBC(MR) and MBC(HR) strains of G. zeae. The resulting Deltabeta(2)tub mutants from both MBC(MR) and MBC(HR) strains grew normally on MBC-free potato dextrose agar medium and were supersensitive to MBC. Complementation of the Deltabeta(2)tub mutants by transformation with a copy of the intact beta(2)tub locus from their parent strains exhibited less resistance than the original strains, and complementation of the Deltabeta(2)tub mutants by transformation with a copy of the intact beta(2)tub locus from sensitive strains restored MBC sensitivity. The results indicated that the mutations in the beta(2)tub gene conferred resistance of G. zeae to benzimidazole fungicides and this gene can be used as a genetic marker in G. zeae.
摘要 禾谷镰孢菌（无性型：赤霉属）引起的小麦赤霉病是中国食品安全的一个威胁，因为收获的谷物受到真菌毒素的污染，这种病害经常发生，而且由于病原菌种群对苯并咪唑类的抗性，一些地区的化学防治也失败了。然而，禾谷镰孢菌对苯并咪唑类杀菌剂（尤其是多菌灵；有效成分：甲基苯并咪唑-2-基氨基甲酸酯[MBC]）的分子抗性机制知之甚少。分析了禾谷镰孢菌中一个β-微管蛋白基因（β（2）tub）（GenBank 登录号：FG06611.1）的 DNA 序列。中度抗性菌株（MBC（MR））中的β（2）tub 突变包括 167 位密码子 TTT（苯丙氨酸）->TAT（酪氨酸）或 200 位密码子 TTC（苯丙氨酸）->TAC（酪氨酸）。一个高度抗性菌株（MBC（HR））有两个点突变，一个位于 73 位密码子 CAG（谷氨酰胺）->CGG（精氨酸），另一个位于 198 位密码子 GAG（谷氨酸）->CTG（亮氨酸）。为了证实β（2）tub 中的突变赋予了对苯并咪唑类杀菌剂的抗性，将 MBC（MR）和 MBC（HR）菌株中的整个β（2）tub 基因座从禾谷镰孢菌中缺失。来自 MBC（MR）和 MBC（HR）菌株的 Deltabeta（2）tub 突变体在不含 MBC 的土豆葡萄糖琼脂培养基上正常生长，对 MBC 超敏。用亲本菌株完整的β（2）tub 基因座的拷贝转化 Deltabeta（2）tub 突变体进行互补，其抗性比原始菌株低，而用敏感菌株完整的β（2）tub 基因座的拷贝转化 Deltabeta（2）tub 突变体恢复了对 MBC 的敏感性。结果表明，β（2）tub 基因突变赋予了禾谷镰孢菌对苯并咪唑类杀菌剂的抗性，该基因可作为禾谷镰孢菌的遗传标记。
