Cell membrane damage, energy dissipation, and ergosterol biosynthesis dysfunction induced by <i>trans</i> -4-methoxycinnamaldehyde inhibits <i>Penicillium digitatum</i> growth

Abstract Citrus green mold (CGM), caused by Penicillium digitatum, is a highly destructive fungal disease that impacts the citrus fruit industry on a global scale, leading to substantial economic losses. As a cinnamaldehyde derivative, trans-4-methoxycinnamaldehyde (MCA) is the preferred alternative for controlling CGM over chemical fungicides because it is less harmful to the environment. In this study, the efficacy of MCA in inhibiting both the mycelial growth and spore germination of P. digitatum was demonstrated. In addition, MCA alleviated CGM in postharvest navel orange fruit. A transcriptomic analysis was conducted to explore the underlying molecular antifungal mechanisms of MCA, revealing 2877 and 3315 differentially expressed genes (DEGs) influenced by MCA treatment at the MIC and minimum fungicidal concentration, respectively. Further Kyoto Encyclopedia of Genes and Genomes pathway analysis of these DEGs indicated that MCA significantly impacted pathways associated with energy metabolism, oxidative stress response, lipid metabolism, and amino acid metabolism—critical elements for sustaining the integrity and normal functioning of the plasma membranes and mitochondria in P. digitatum cells. Our biochemical assays, as well as observations via electron microscopy and propidium iodide staining, demonstrated that the MCA treatment modified mycelial morphology, altered conidial ultra-structure, compromised plasma membrane integrity, and hindered mitochondrial function and ergosterol biosynthesis. Collectively, these findings enhance the understanding of MCA’s antifungal activity through its molecular mechanisms, positioning it as a promising agent for controlling postharvest CGM in citrus fruits.