Sterol biosynthesis is regulated by a sophisticated regulatory network involving multiple transcription factors in fungi

Ergosterol, a pivotal constituent of the fungal cell membrane, plays a crucial role in diverse cellular activities. Fungi inherently regulate ergosterol homeostasis, a process traditionally associated with the control of a major transcription factor, like SREBP, activated in response to ergosterol depletion, regardless of which ergosterol biosynthesis step is affected. Contrary to the established paradigm, our investigation demonstrates that the inhibition of ergosterol biosynthesis at specific steps triggers distinct transcriptional responses in erg genes across fungi, including Neurospora crassa, Aspergillus fumigatus, and Fusarium verticillioides. In N. crassa, the targeted responses are orchestrated by several transcription factors that have undergone functional rewiring. Specifically, ERG24 inhibition by amorolfine activates transcription factors SAH-2 and AtrR, resulting in the upregulation of erg24, erg2, erg25 and erg3. Additionally, ERG11 inhibition by azoles activates transcription factor NcSR, leading to the upregulation of erg11 and erg6. Our findings unveil a novel sophisticated regulation model of sterol biosynthesis in fungi which potentially enhances fungal survival in complex environments, thus providing new insights into sterol homeostasis maintenance and a deeper understanding of drug resistance mechanisms in fungi. Overall design: To thoroughly investigate the targeted regulatory mechanism of ergosterol biosynthesis, we sequenced the transcriptome of N.crassa treated with various sterol synthesis inhibitors. Additionally, we analyzed the gene expression profiles of three key transcription factors—SAH-2 (NCU04731), AtrR (NCU01478), and NcSR (NCU08594)—in knockout strains using data from RNA-seq.