# The chromatin remodeling factor Arp9 modulates drug-resistance and plays a key role in aflatoxins biosynthesis under mammalian-physiological-temperature in Aspergillus flavus

## TL;DR

This study shows that the Arp9 protein in Aspergillus flavus affects drug resistance and aflatoxin production at body temperatures, offering new insights for treating fungal infections.

## Contribution

The study reveals that Arp9 modulates drug resistance and aflatoxin biosynthesis in A. flavus under mammalian physiological temperatures.

## Key findings

- Arp9 enhances sensitivity to amphotericin B by increasing ergosterol synthesis.
- Arp9 reduces voriconazole resistance by down-regulating Erg11A expression.
- Arp9 promotes aflatoxin B1 biosynthesis at 35°C and 37°C, especially in drug-resistant strains.

## Abstract

Aspergillus flavus is the second most prevalent species of Aspergillus causing invasive aspergillosis, but its treatment efforts had been hindered by the continuous emergence of drug-resistant fungal strains, while the underlying mechanisms remain largely unexplored. In this study, we investigated the role of the chromatin remodeling factor Arp9 in A. flavus drug-resistant. We show that Arp9 up-regulates the chromatin accessibility of the Erg3 and Erg6 promoters, thereby increasing their transcription levels and enhancing ergosterol synthesis. Therefore, the absence of Arp9 enhances A. flavus sensitivity to amphotericin B (AMB). Additionally, by down-regulating chromatin accessibility of Erg11A gene promoter, Arp9 leads to the decrease of its transcription level and subsequently reduces A. flavus resistance to voriconazole (VOR). Co-immunoprecipitation analysis revealed that Arp9 exists in both SWI/SNF and RSC complex. Drug susceptibility test results indicated that the drug sensitivity response induced by Arp9 may be unique to Arp9, as neither SWP82 of the SWI/SNF nor Sth1 of the RSC is required. The role of Arp9 in drug-resistance was also confirmed using the Galleria mellonella model. Furthermore, we found that VOR induces aflatoxin B1 (AFB1) biosynthesis in an Arp9-dependent manner at 35°C and 37°C, and the effect is dramatically magnified in the VOR-resistant A. flavus strain. This study demonstrates that Arp9 plays a critical role in regulating fungal drug-resistance in vitro and in vivo and revealed that Arp9 is an important factor in enhancing AFB1 biosynthesis under Mammalian physiological temperatures. This study provides potential new insights for the control of the infections caused by filamentous pathogenic fungi.

As the notorious aflatoxin producing pathogenic fungi in agriculture and medicine, Aspergillus flavus is widely distributed, contaminating various crops, and inducing invasive aspergillosis mainly to immunodeficiency-patients. Since the drug-resistant clinical A. flavus strains is continuously emergent, the underlying mechanisms urgently needs to be explored. This study demonstrates that chromatin remodeling factor Arp9 is a key switch in A. flavus drug-resistance. It reduces the resistance of A. flavus to VOR by down-regulating the expression of Erg11A. Additionally, Arp9 decreases the sensitivity of A. flavus to AMB by up-regulating ergosterol synthesis. And the role of Arp9 in drug-resistance in vivo was further verified by the G. mellonella model. More importantly, our study is the first to discover that Arp9 promotes AFB1 biosynthesis at mammalian physiological temperature (from 35°C to 37°C) under VOR stress, especially in VOR-resistant strain. This study reveals the important role of chromatin remodeling factor Arp9 in fungal drug-resistance, and provides a potential key target for the treatment of A. flavus infections.