Light regulation is critical in fungal growth, development, morphogenesis, secondary metabolism, and the biological clock. The fungus Elsinoë arachidis is known to produce the mycotoxin Elsinochrome (ESC), a key factor contributing to its pathogenicity, under light conditions. Although previous studies have predominantly focused on the light-induced production of ESC and its biosynthetic pathways, the detailed mechanisms underlying this process remain largely unexplored. This study explores the influence of light on ESC production and gene expression in E. arachidis. Under white light exposure for 28 days, the ESC yield was observed to reach 33.22 nmol/plug. Through transcriptome analysis, 5925 genes were identified as differentially expressed between dark and white light conditions, highlighting the significant impact of light on gene expression. Bioinformatics identified specific light-regulated genes, including eight photoreceptor genes, five global regulatory factors, and a cluster of 12 genes directly involved in the ESC biosynthesis, with expression trends confirmed by RT-qPCR. In conclusion, the study reveals the substantial alteration in gene expression associated with ESC biosynthesis under white light and identifies potential candidates for in-depth functional analysis. These findings advance understanding of ESC biosynthesis regulation and suggest new strategies for fungal pathogenicity control.

The filamentous fungus Elsinoë arachidis is a major foliar pathogen responsible for peanut scab, which is a significant disease affecting commercial peanut cultivation. Elsinochrome (ESC), produced by numerous phytopathogenic Elsinoë species, is a non-host-selective polyketide phytotoxin with strong photosensitive activity and plays a crucial role in pathogenesis on host plants. In E. arachidis, a dual-domain enzyme encoded by the gene ESCB3, containing both O-methyltransferase and a FAD-dependent monooxygenase domain, has been identified. To elucidate the role of ESCB3, the biological function, expression pattern of the ESC biosynthesis gene cluster, and associated metabolomics analyses were investigated in the present study. An ESCB3 deletion mutant (Δ ESCB3) was created by targeted gene disruption. Notably, ESC production was completely blocked in the Δ ESCB3 mutant, and the expression of ESC biosynthetic genes, except for the polyketide synthase gene ESCB1, was significantly downregulated. Additionally, the Δ ESCB3 exhibited heightened sensitivity to multiple stress tolerance compared with the wild type, especially oxidative stress/H ₂ O ₂ , highlighting the crucial role of ESCB3 in growth, development, and ESC biosynthesis in E. arachidis. Pathogenicity assays revealed a significant reduction in the pathogenicity of the Δ ESCB3 mutant, suggesting a possible correlation with the suppressed biosynthesis of ESC. Metabolomic analyses further confirmed that ESCB3 is indispensable for the ESC biosynthetic process and acts as a key regulatory factor. Collectively, the results of this study provide significant insights into the molecular mechanisms governing ESCB3-mediated virulence and ESC production in E. arachidis, offering potential targets for disease control strategies in peanut scab. [ ] Copyright © 2026 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .