## 4 Discussion
A literature survey revealed that 8 out of 15 pure compounds were previously reported in the _Fusarium_ genera, including \(p\)-hydroxybenzaldehyde, 2-(4-hydroxyphenyl)ethanol, phenylacetic acid, daidzein, \(\beta\)-2\({}^{\prime}\)-deoxyadenosine, \(\beta\)-adenosine, indole-3-acetic acid, and salicylic acid [1; 34; 35]. Based on these findings, it seems that the metabolic profile of AQF6 may be unique due to endophytic lifestyle and horizontal gene transfer during co-evolution. Since only one genome sequence of _F. foetens_ NRRL 38302 is available on the Genbank database to date, genomic structure, fungus-plant interactions, and the biosynthetic gene clusters of AQF6 through whole-genome sequencing and genome mining will be interesting subjects for future studies. In free-radical scavenging assays, five known compounds showed potent in vitro antioxidant activities, including 2-(4-hydroxyphenyl)ethanol (tyrosol), salicylic acid, isoformononontein, \(p\)-hydroxybenzaldehyde, and phenylacetic acid. Isoformonontein is known as a methoxydaidzein produced only by actinomycetes such as _Nocardi_ sp. NRRL 5646 and _Amyclotopsis_ sp. YIM 130642 [36]. Despite the lack of in vitro antioxidant-activity evidence, isoformontein treatment led to significant decrease in ROS production through inhibition of the NLRP3/ASC/IL-1 axis, which prevented streptozotocin-induced neuroinflammation in the rat model [37]. Salicylic acid functions as a phenolic phytothormone, contributing to protection against oxidative stress through the activation of the antioxidant system of plants [38]. In contrast, \(p\)-hydroxybenzaldehyde has in vitro antioxidant activity against _ABTS\({}^{\star\star}\)_(0.96 uM Trolox equivalents/g) and peroxyl radicals (27.58 mM Trolox equivalents/g) [39]. The DPPH and hydroxyl radical-scavenging activities of 2-(4-hydroxyphenyl)ethanol obtained from our study was comparable to that of _Fusarium solani_ PQF9 [2]. Of note, antioxidant activity of phenylacetic acid has not been reported yet, to date. Taken together, these results further confirmed that the endophytic fungus _F. foetens_ AQF6 is a producer of antioxidant metabolites. An important finding of the present study was the identification of FUS. Endophytic _Fusarium_ spp. have been demonstrated to produce a number of sesquiterpenes including fusanoid, fusarticrin, and agripilol which exhibit antimicrobial and anticancer activities [35]. Using the _S. cerevisiae_ cell model, FUS was proved to be safe, and alleviated H\({}_{2}\)O\({}_{2}\)-induced oxidative stress. Similar to this study, plant-derived compounds such as quercetin, step-pogenin, and morin improved the tolerance of _S. cerevisiae_ BY4741 to oxidative stress provoked by acetic acid [6]. It is possible that the protective effect of FUS on yeast cells resulted from the direct neutralization of H\({}_{2}\)O\({}_{2}\) or the expression of enzymatic and non-enzymatic scavengers. Thus, the detection of ROS, enzymatic activities, expression levelsof antioxidant markers such as catalase, glutaredoxin, and superoxide dismutase, and the survival of antioxidant-deficient mutants in response to oxidative stress under the protection of FUS are required to demonstrate the mode of action of FUS in future studies.