Sharma Aashish Kumar, Kumar Adesh, Rijal Robin
Department of Plant Pathology, School of Agriculture, Lovely Professional University, Phagwara, Punjab 144411, India.
Department of Plant Pathology, School of Agriculture, Lovely Professional University, Phagwara, Punjab 144411, India.
Gene. 2025 Feb 10;937:149151. doi: 10.1016/j.gene.2024.149151. Epub 2024 Dec 9.
Aspergillus species produce polyketides, which form the basis of aflatoxins, some of the most significant mycotoxins in agriculture. Aflatoxins contaminate cereals, oilseeds, and nuts, both in the field and during storage. Of the 13 naturally occurring aflatoxins, the most potent are aflatoxins B, B, G, and G. The primary aflatoxigenic species are A. flavus, A. parasiticus, and A. nomius, while A. arachidicola, A. minisclerotigenes, and A. saccharicola also documented. These aflatoxin producers belong to three sections- 'Flavi', 'Ochraceorosei', and 'Nidulantes.' Aspergillus flavus, within section Flavi, shows morphological diversity, classified into Group I (S- and L- strains) and Group II (S- strains), with S-strains producing higher levels of aflatoxins. Aflatoxin biosynthesis is primarily regulated by the aflR gene, though other genes like aflS, aflP, aflQ, aflC, and aflM are also associated. However, presence of the aflR gene does not guarantee aflatoxin production across species. Sterigmatocystin serves as a precursor molecule within the pathway leading to aflatoxin production. Phylogenetic assessment, using ITS, BenA, CaM, and RBP2 gene sequences, reveals distinct clusters within Aspergillus sections and highlights the co-evolution of aflatoxigenic and non-aflatoxigenic species. Aspergillus ochraceoroseus and A. rambellii diverged out of aflatoxin-producing species earlier in evolutionary history, before splitting from a shared ancestor with A. fumigatus, which neither produces aflatoxins nor sterigmatocystin. Non-aflatoxigenic species like A. oryzae may evolve from aflatoxigenic species like A. flavus due to variations in evolutionary rates, telomere deletions, and mutations in aflatoxin biosynthesis genes. Comparative genomic analysis of AF, AF/ST and ST gene cluster shows that A. flavus has a larger aflatoxin gene cluster, while A. ochraceoroseus lacks the genes aflP and aflQ. Additionally, A. ochraceoroseus and A. rambellii possess a smaller genome, suggesting that genetic drift and deletions have refined their genomes for more efficient aflatoxin production.
曲霉属物种产生聚酮化合物，这些聚酮化合物构成了黄曲霉毒素的基础，黄曲霉毒素是农业中一些最重要的霉菌毒素。黄曲霉毒素在田间和储存期间都会污染谷物、油籽和坚果。在13种天然存在的黄曲霉毒素中，毒性最强的是黄曲霉毒素B1、B2、G1和G2。主要产黄曲霉毒素的物种是黄曲霉、寄生曲霉和诺米曲霉，同时也记录到了花生曲霉、小菌核曲霉和糖曲霉。这些产黄曲霉毒素的物种属于三个组——“黄组”、“赭色玫瑰组”和“构巢组”。黄组中的黄曲霉表现出形态多样性，分为第一组（S型和L型菌株）和第二组（S型菌株），其中S型菌株产生的黄曲霉毒素水平更高。黄曲霉毒素的生物合成主要受aflR基因调控，不过其他基因如aflS、aflP、aflQ、aflC和aflM也与之相关。然而，aflR基因的存在并不能保证所有物种都能产生黄曲霉毒素。柄曲霉素是导致黄曲霉毒素产生的途径中的前体分子。利用ITS、BenA、CaM和RBP2基因序列进行的系统发育评估揭示了曲霉属各组中的不同聚类，并突出了产黄曲霉毒素和不产黄曲霉毒素物种的共同进化。赭色曲霉和兰氏曲霉在进化历史早期就从产黄曲霉毒素的物种中分化出来，然后才与既不产生黄曲霉毒素也不产生柄曲霉素的烟曲霉从共同祖先中分离出来。像米曲霉这样的不产黄曲霉毒素的物种可能由于进化速率的变化、端粒缺失以及黄曲霉毒素生物合成基因的突变而从像黄曲霉这样的产黄曲霉毒素的物种进化而来。对AF、AF/ST和ST基因簇的比较基因组分析表明，黄曲霉有一个更大的黄曲霉毒素基因簇，而赭色曲霉缺乏aflP和aflQ基因。此外，赭色曲霉和兰氏曲霉的基因组较小，这表明基因漂变和缺失对它们的基因组进行了优化，以实现更高效的黄曲霉毒素产生。
