Institute of Biotechnology, Zhejiang University, 866 Yuhangtang Road, Hangzhou, 310058, China.
Mol Plant Pathol. 2013 Jan;14(1):71-83. doi: 10.1111/j.1364-3703.2012.00829.x. Epub 2012 Sep 4.
The ergosterol biosynthesis pathway is well understood in Saccharomyces cerevisiae, but currently little is known about the pathway in plant-pathogenic fungi. In this study, we characterized the Fusarium graminearum FgERG4 gene encoding sterol C-24 reductase, which catalyses the conversion of ergosta-5,7,22,24-tetraenol to ergosterol in the final step of ergosterol biosynthesis. The FgERG4 deletion mutant ΔFgErg4-2 failed to synthesize ergosterol. The mutant exhibited a significant decrease in mycelial growth and conidiation, and produced abnormal conidia. In addition, the mutant showed increased sensitivity to metal cations and to various cell stresses. Surprisingly, mycelia of ΔFgErg4-2 revealed increased resistance to cell wall-degrading enzymes. Fungicide sensitivity tests revealed that ΔFgErg4-2 showed increased resistance to various sterol biosynthesis inhibitors (SBIs), which is consistent with the over-expression of SBI target genes in the mutant. ΔFgErg4-2 was impaired dramatically in virulence, although it was able to successfully colonize flowering wheat head and tomato, which is in agreement with the observation that the mutant produces a significantly lower level of trichothecene mycotoxins than does the wild-type progenitor. All of these phenotypic defects of ΔFgErg4-2 were complemented by the reintroduction of a full-length FgERG4 gene. In addition, FgERG4 partially rescued the defect of ergosterol biosynthesis in the Saccharomyces cerevisiae ERG4 deletion mutant. Taken together, the results of this study indicate that FgERG4 plays a crucial role in ergosterol biosynthesis, vegetative differentiation and virulence in the filamentous fungus F. graminearum.
麦角甾醇生物合成途径在酿酒酵母中得到了很好的理解，但目前对植物病原真菌中的途径知之甚少。在这项研究中，我们对编码甾醇 C-24 还原酶的禾谷镰刀菌 FgERG4 基因进行了表征，该酶在麦角甾醇生物合成的最后一步催化麦角甾-5,7,22,24-四烯醇转化为麦角甾醇。FgERG4 缺失突变体 ΔFgErg4-2 无法合成麦角甾醇。该突变体的菌丝生长和产孢能力显著下降，产生异常的分生孢子。此外，该突变体对金属阳离子和各种细胞应激的敏感性增加。令人惊讶的是，ΔFgErg4-2 的菌丝显示出对细胞壁降解酶的抗性增加。杀菌剂敏感性测试表明，ΔFgErg4-2 对各种甾醇生物合成抑制剂（SBIs）表现出更高的抗性，这与突变体中 SBI 靶基因的过度表达一致。ΔFgErg4-2 的毒力显著受损，尽管它能够成功定植开花小麦头部和番茄，这与突变体产生的三萜类霉菌毒素水平明显低于野生型亲本的观察结果一致。ΔFgErg4-2 的所有这些表型缺陷都通过全长 FgERG4 基因的重新引入得到了弥补。此外，FgERG4 部分挽救了酿酒酵母 ERG4 缺失突变体中麦角甾醇生物合成的缺陷。综上所述，这项研究的结果表明，FgERG4 在丝状真菌禾谷镰刀菌中麦角甾醇生物合成、营养分化和毒力中发挥着关键作用。
