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Identification and functional analysis of the aspergillic acid gene cluster in Aspergillus flavus.
Fungal Genetics and Biology ( IF 3 ) Pub Date : 2018-04-21 , DOI: 10.1016/j.fgb.2018.04.009
Matthew D Lebar 1 , Jeffrey W Cary 1 , Rajtilak Majumdar 1 , Carol H Carter-Wientjes 1 , Brian M Mack 1 , Qijian Wei 1 , Valdet Uka 2 , Sarah De Saeger 2 , José Diana Di Mavungu 2
Affiliation  

Aspergillus flavus can colonize important food staples and produce aflatoxins, a group of toxic and carcinogenic secondary metabolites. Previous in silico analysis of the A. flavus genome revealed 56 gene clusters predicted to be involved in the biosynthesis of secondary metabolites. A. flavus secondary metabolites produced during infection of maize seed are of particular interest, especially with respect to their roles in the biology of the fungus. A predicted nonribosomal peptide synthetase-like (NRPS-like) gene, designated asaC (AFLA_023020), present in the uncharacterized A. flavus secondary metabolite gene cluster 11 was previously shown to be expressed during the earliest stages of maize kernel infection. Cluster 11 is composed of six additional genes encoding a number of putative decorating enzymes as well as a transporter and transcription factor. We generated knock-out mutants of the seven predicted cluster 11 genes. LC-MS analysis of extracts from knockout mutants of these genes showed that they were responsible for the synthesis of the previously characterized antimicrobial mycotoxin aspergillic acid. Extracts of the asaC mutant showed no production of aspergillic acid or its precursors. Knockout of the cluster 11 P450 oxidoreductase afforded a pyrazinone metabolite, the aspergillic acid precursor deoxyaspergillic acid. The formation of hydroxyaspergillic acid was abolished in a desaturase/hydroxylase mutant. The hydroxamic acid functional group in aspergillic acid allows the molecule to bind to iron resulting in the production of a red pigment in A. flavus identified previously as ferriaspergillin. A reduction of aflatoxin B1 and cyclopiazonic acid that correlated with reduced fungal growth was observed in maize kernel infection assays when aspergillic acid biosynthesis in A. flavus is halted.

中文翻译:

黄曲霉中曲霉酸基因簇的鉴定和功能分析。

黄曲霉能在重要的食物主食上定殖,并产生黄曲霉毒素,黄曲霉毒素是一组有毒和致癌的次生代谢产物。先前对黄曲霉基因组进行的计算机分析表明,预计有56个基因簇参与次级代谢产物的生物合成。玉米种子感染过程中产生的黄曲霉次生代谢产物特别令人关注,尤其是它们在真菌生物学中的作用方面。以前显示在未表征的黄曲霉次生代谢产物基因簇11中存在一个称为aC(AFLA_023020)的预测的非核糖体肽合成酶样(NRPS-like)基因,该基因在玉米粒感染的最早阶段表达。簇11由六个其他基因组成,这些基因编码许多假定的修饰酶以及转运蛋白和转录因子。我们生成了七个预测的簇11基因的敲除突变体。这些基因的敲除突变体的提取物的LC-MS分析表明,它们负责合成先前表征的抗微生物真菌毒素曲霉酸。asaC突变体的提取物未产生曲霉酸或其前体。敲除簇11 P450氧化还原酶,得到吡嗪酮代谢物,即曲霉酸前体脱氧曲霉酸。在去饱和酶/羟化酶突变体中消除了羟戊酸的形成。曲霉酸中的异羟肟酸官能团使该分子与铁结合,从而在黄曲霉中产生红色颜料,该色素以前被鉴定为亚铁精蛋白。当黄曲霉中曲霉酸的生物合成被停止时,在玉米仁感染试验中观察到黄曲霉毒素B1和环吡嗪酸的减少与真菌生长减少有关。
更新日期:2019-11-01
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