Ramamoorthy Vellaisamy, Cahoon Edgar B, Thokala Mercy, Kaur Jagdeep, Li Jia, Shah Dilip M
Donald Danforth Plant Science Center, 975 North Warson Road, St Louis, MO 63132, USA.
Eukaryot Cell. 2009 Feb;8(2):217-29. doi: 10.1128/EC.00255-08. Epub 2008 Nov 21.
The C-9-methylated glucosylceramides (GlcCers) are sphingolipids unique to fungi. They play important roles in fungal growth and pathogenesis, and they act as receptors for some antifungal plant defensins. We have identified two genes, FgMT1 and FgMT2, that each encode a putative sphingolipid C-9 methyltransferase (C-9-MT) in the fungal pathogen Fusarium graminearum and complement a Pichia pastoris C-9-MT-null mutant. The DeltaFgmt1 mutant produced C-9-methylated GlcCer like the wild-type strain, PH-1, whereas the DeltaFgmt2 mutant produced 65 to 75% nonmethylated and 25 to 35% methylated GlcCer. No DeltaFgmt1DeltaFgmt2 double-knockout mutant producing only nonmethylated GlcCer could be recovered, suggesting that perhaps C-9-MTs are essential in this pathogen. This is in contrast to the nonessential nature of this enzyme in the unicellular fungus P. pastoris. The DeltaFgmt2 mutant exhibited severe growth defects and produced abnormal conidia, while the DeltaFgmt1 mutant grew like the wild-type strain, PH-1, under the conditions tested. The DeltaFgmt2 mutant also exhibited drastically reduced disease symptoms in wheat and much-delayed disease symptoms in Arabidopsis thaliana. Surprisingly, the DeltaFgmt2 mutant was less virulent on different host plants tested than the previously characterized DeltaFggcs1 mutant, which lacks GlcCer synthase activity and produces no GlcCer at all. Moreover, the DeltaFgmt1 and DeltaFgmt2 mutants, as well as the P. pastoris strain in which the C-9-MT gene was deleted, retained sensitivity to the antifungal plant defensins MsDef1 and RsAFP2, indicating that the C-9 methyl group is not a critical structural feature of the GlcCer receptor required for the antifungal action of plant defensins.
C-9-甲基化葡糖神经酰胺（GlcCers）是真菌特有的鞘脂类。它们在真菌生长和致病过程中发挥重要作用，并且作为一些抗真菌植物防御素的受体。我们已经鉴定出两个基因，FgMT1和FgMT2，它们在真菌病原体禾谷镰刀菌中各自编码一种假定的鞘脂C-9甲基转移酶（C-9-MT），并能互补毕赤酵母C-9-MT缺失突变体。ΔFgmt1突变体与野生型菌株PH-1一样产生C-9-甲基化GlcCer，而ΔFgmt2突变体产生65%至75%的非甲基化GlcCer和25%至35%的甲基化GlcCer。无法获得仅产生非甲基化GlcCer的ΔFgmt1ΔFgmt2双敲除突变体，这表明C-9-MT可能在这种病原体中是必需的。这与该酶在单细胞真菌毕赤酵母中的非必需性质形成对比。ΔFgmt2突变体表现出严重的生长缺陷并产生异常分生孢子，而ΔFgmt1突变体在测试条件下的生长与野生型菌株PH-1相似。ΔFgmt2突变体在小麦中还表现出疾病症状大幅减轻，在拟南芥中疾病症状出现延迟很多。令人惊讶的是，与先前表征的缺乏GlcCer合酶活性且根本不产生GlcCer的ΔFggcs1突变体相比，ΔFgmt2突变体在测试的不同寄主植物上的毒力更低。此外，ΔFgmt1和ΔFgmt2突变体以及缺失C-9-MT基因的毕赤酵母菌株对抗真菌植物防御素MsDef1和RsAFP2仍保持敏感性，这表明C-9甲基基团不是植物防御素抗真菌作用所需的GlcCer受体的关键结构特征。
