Transcriptional Suppression of Five Critical Biosynthetic Enzyme Genes Contributes to Disruption of AFB1 Production in Aspergillus oryzae XJ-1, a Locust Biological Control Agent

Aspergillus oryzae XJ-1 is a highly pathogenic fungus against locusts. Many Aspergillus flavus strains could produce aflatoxin (AF), a serious toxin and unsafe for mammals. Due to belonging to the same genus as A. flavus, whether A. oryzae XJ-1 produces AF has been questioned. This is important for further development as a biological control agent. In this study, we first tested AFB1 production from four strains, A. oryzae XJ-1 (A. oryzae XJ-1), non-aflatoxigenic A. oryzae (NAF A. oryzae) (CGMCC: 3.9544), non-aflatoxigenic A. flavus (NAF A. flavus) (CGMCC: 3.3950), and aflatoxin-producing A. flavus (AF A. flavus) (CGMCC: 3.4408), with high-performance liquid chromatography–fluorescence detection (HPLC-FLD). Then, transcriptome sequencing and bioinformation analysis, reverse transcription PCR (RT-PCR), and quantitative real-time reverse transcription PCR (RT-qPCR) were used to reveal the transcript expression of key genes in the biosynthesis of AF in the above four strains. The level of AF in A. oryzae XJ-1, like the other two non-AF producing strains, was significantly lower than in AF A. flavus that produces AF. Although the 22 aflatoxin-related genes were present within the gene clusters of both strains, the transcript levels of five critical biosynthetic enzyme genes (aflG, aflL, aflP, aflQ, aflK) were significantly lower in A. oryzae XJ-1 than in AF A. flavus, explaining why A. oryzae XJ-1 does not produce AFB1. These preliminary results indicate that A. oryzae XJ-1 may be safe for mammals and has potential as an environmentally friendly biocontrol agent for locust management.