Kim Jong H, Yu Jiujiang, Mahoney Noreen, Chan Kathleen L, Molyneux Russell J, Varga John, Bhatnagar Deepak, Cleveland Thomas E, Nierman William C, Campbell Bruce C
Plant Mycotoxin Research Unit, Western Regional Research Center, USDA-ARS, 800 Buchanan St., Albany, CA 94710, USA.
Int J Food Microbiol. 2008 Feb 29;122(1-2):49-60. doi: 10.1016/j.ijfoodmicro.2007.11.058. Epub 2007 Nov 29.
Caffeic acid (3,4-dihydroxycinnamic acid, 12 mM) added to a fat-based growth medium reduces >95% of aflatoxin production by Aspergillus flavus NRRL 3357, without affecting fungal growth. Microarray analysis of caffeic acid-treated A. flavus indicated expression of almost all genes in the aflatoxin biosynthetic cluster were down-regulated, ranging from a log2 ratio of caffeic acid treated and untreated of -1.12 (medium) to -3.13 (high). The only exceptions were genes norB and the aflatoxin pathway regulator-gene, aflJ, which showed low expression levels in both treated and control fungi. The secondary metabolism regulator-gene, laeA, also showed little change in expression levels between the fungal cohorts. Alternatively, expression of genes in metabolic pathways (i.e., amino acid biosynthesis, metabolism of aromatic compounds, etc.) increased (log2 ratio >1.5). The most notable up-regulation of A. flavus expression occurred in four genes that are orthologs of the Saccharomyces cerevisiae AHP1 family of genes. These genes encode alkyl hydroperoxide reductases that detoxify organic peroxides. These increases ranged from a log2 ratio of 1.08 to 2.65 (moderate to high), according to real-time quantitative reverse transcription-PCR (qRT-PCR) assays. Based on responses of S. cerevisiae gene deletion mutants involved in oxidative stress response, caffeic, chlorogenic, gallic and ascorbic acids were potent antioxidants under oxidative stress induced by organic peroxides, tert-butyl and cumene hydroperoxides. Differential hypersensitivity to these peroxides and hydrogen peroxide occurred among different mutants in addition to their ability to recover with different antioxidants. These findings suggest antioxidants may trigger induction of genes encoding alkyl hydroperoxide reductases in A. flavus. The possibilities that induction of these genes protects the fungus from oxidizing agents (e.g., lipoperoxides, reactive oxygen species, etc.) produced during host-plant infection and this detoxification attenuates upstream signals triggering aflatoxigenesis are discussed.
添加到脂肪基生长培养基中的咖啡酸（3,4 - 二羟基肉桂酸，12 mM）可使黄曲霉NRRL 3357的黄曲霉毒素产量降低95%以上，且不影响真菌生长。对经咖啡酸处理的黄曲霉进行微阵列分析表明，黄曲霉毒素生物合成簇中几乎所有基因的表达均下调，咖啡酸处理组与未处理组的log2比值范围为 -1.12（中等）至 -3.13（高）。唯一的例外是norB基因和黄曲霉毒素途径调节基因aflJ，它们在处理过的真菌和对照真菌中均表现出低表达水平。次生代谢调节基因laeA在两组真菌中的表达水平也几乎没有变化。另外，代谢途径（即氨基酸生物合成、芳香族化合物代谢等）中的基因表达增加（log2比值>1.5）。黄曲霉表达上调最显著的是四个与酿酒酵母AHP1基因家族直系同源的基因。这些基因编码可使有机过氧化物解毒的烷基过氧化氢还原酶。根据实时定量逆转录 - PCR（qRT - PCR）分析，这些基因的增加幅度在log2比值1.08至2.65之间（中等至高）。基于参与氧化应激反应的酿酒酵母基因缺失突变体的反应，咖啡酸、绿原酸、没食子酸和抗坏血酸在由有机过氧化物、叔丁基过氧化氢和异丙苯过氧化氢诱导的氧化应激下是有效的抗氧化剂。除了它们用不同抗氧化剂恢复的能力外，不同突变体对这些过氧化物和过氧化氢的超敏反应也存在差异。这些发现表明抗氧化剂可能会触发黄曲霉中编码烷基过氧化氢还原酶的基因的诱导。本文讨论了这些基因的诱导是否能保护真菌免受宿主植物感染期间产生的氧化剂（如脂过氧化物、活性氧等）的侵害，以及这种解毒作用是否会减弱触发黄曲霉毒素生成的上游信号的可能性。
