Wavelength-dependent regulation of Penicillium expansum: red and green light promote fungal fitness and patulin accumulation via metabolic homeostasis.

Light-based regulation is increasingly employed as an environmentally sustainable physical intervention for preserving postharvest agricultural commodities during storage and transit. Nevertheless, incident light can concurrently modulate the physiological and biochemical dynamics of phytopathogenic fungi, thereby introducing unintended risks to preservation outcomes. In this study, we constructed a customized illumination system integrating discrete wavelengths (green light: 540 nm; red light: 660 nm) and photoperiods (DD, control: continuous darkness; LD: 12 h light/12 h dark cycles; LL: continuous light) to systematically evaluate the impact of light parameters on the development of Penicillium expansum, and to elucidate the mechanistic underpinnings of its photoresponsive behavior. Results showed that both red and green light significantly promoted fungal development. Conidial germination rates increased from 50.43% (DD) to 55.67% (R-LL) and 65.42% (G-LL), respectively. Mycelial growth, sporulation, and PAT production were also markedly enhanced under light exposure. PAT accumulation reached approximately six-fold higher than the control during the early stage (36 h), and remained about two-fold higher at 60 h (R-LL, R-LD, G-LL, G-LD). These phenotypic responses may be attributed to three principal regulatory processes: Enhanced cellular energy metabolism, which supplies the requisite bioenergetic capacity for growth and development; Activation of lipid metabolic pathways coupled with maintenance of redox homeostasis, which collectively facilitate sporulation; Elevated activities of key metabolic enzymes coincident with transcriptional upregulation of genes governing vegetative growth, developmental progression, and mycotoxin biosynthesis. Collectively, these findings provide a theoretical foundation for optimizing light parameters in postharvest photobiological systems and for mitigating the associated risks of fungal contamination.