Bhatnagar Deepak, Cary Jeffrey W, Ehrlich Kenneth, Yu Jiujiang, Cleveland Thomas E
Food and Feed Safety Research Unit, U.S.D.A., A.R.S., Southern Regional Research Center, New Orleans, LA 70124, USA.
Mycopathologia. 2006 Sep;162(3):155-66. doi: 10.1007/s11046-006-0050-9.
Aflatoxins are polyketide-derived, toxic, and carcinogenic secondary metabolites produced primarily by two fungal species, Aspergillus flavus and A. parasiticus, on crops such as corn, peanuts, cottonseed, and treenuts. Regulatory guidelines issued by the U.S. Food and Drug Administration (FDA) prevent sale of commodities if contamination by these toxins exceeds certain levels. The biosynthesis of these toxins has been extensively studied. About 15 stable precursors have been identified. The genes involved in encoding the proteins required for the oxidative and regulatory steps in the biosynthesis are clustered in a 70 kb portion of chromosome 3 in the A. flavus genome. With the characterization of the gene cluster, new insights into the cellular processes that govern the genes involved in aflatoxin biosynthesis have been revealed, but the signaling processes that turn on aflatoxin biosynthesis during fungal contamination of crops are still not well understood. New molecular technologies, such as gene microarray analyses, quantitative polymerase chain reaction (PCR), and chromatin immunoprecipitation are being used to understand how physiological stress, environmental and soil conditions, receptivity of the plant, and fungal virulence lead to episodic outbreaks of aflatoxin contamination in certain commercially important crops. With this fundamental understanding, we will be better able to design improved non-aflatoxigenic biocompetitive Aspergillus strains and develop inhibitors of aflatoxin production (native to affected crops or otherwise) amenable to agricultural application for enhancing host-resistance against fungal invasion or toxin production. Comparisons of aflatoxin-producing species with other fungal species that retain some of the genes required for aflatoxin formation is expected to provide insight into the evolution of the aflatoxin gene cluster, and its role in fungal physiology. Therefore, information on how and why the fungus makes the toxin will be valuable for developing an effective and lasting strategy for control of aflatoxin contamination.
黄曲霉毒素是一类由聚酮衍生的、有毒且致癌的次生代谢产物，主要由黄曲霉和寄生曲霉这两种真菌在玉米、花生、棉籽和坚果等作物上产生。美国食品药品监督管理局（FDA）发布的监管指南规定，如果这些毒素的污染超过一定水平，将禁止相关商品的销售。人们对这些毒素的生物合成进行了广泛研究，已鉴定出约15种稳定的前体物质。参与黄曲霉毒素生物合成氧化和调控步骤所需蛋白质编码的基因，聚集在黄曲霉菌基因组第3号染色体70 kb的区域内。随着该基因簇的表征，人们对控制黄曲霉毒素生物合成相关基因的细胞过程有了新的认识，但在作物受真菌污染期间开启黄曲霉毒素生物合成的信号传导过程仍未得到充分理解。基因微阵列分析、定量聚合酶链反应（PCR）和染色质免疫沉淀等新的分子技术，正被用于了解生理应激、环境和土壤条件、植物的易感性以及真菌毒力如何导致某些重要商业作物中黄曲霉毒素污染的偶发性爆发。有了这一基本认识，我们将更有能力设计改良的非产黄曲霉毒素的生物竞争性曲霉菌株，并开发黄曲霉毒素产生的抑制剂（来源于受影响作物或其他途径），使其适用于农业应用，以增强宿主对真菌入侵或毒素产生的抗性。将产黄曲霉毒素的物种与保留黄曲霉毒素形成所需部分基因的其他真菌物种进行比较，有望深入了解黄曲霉毒素基因簇的进化及其在真菌生理学中的作用。因此，关于真菌如何以及为何产生毒素的信息，对于制定控制黄曲霉毒素污染的有效且持久策略将具有重要价值。
