Investigating the Mechanisms Underlying Citral-Induced Oxidative Stress and Its Contribution to Antifungal Efficacy on Magnaporthe oryzae Through a Multi-Omics Approach

Citral, an organic compound found in lemongrass (<i>Cymbopogon citratus</i>) oil and <i>Litsea cubeba</i> essential oil, has been reported to exhibit notable antifungal activity against <i>Magnaporthe oryzae</i> (<i>M. oryzae</i>), the pathogen of rice blast, which causes significant economic losses in rice production. However, the role of citral in inducing oxidative stress related to antifungal ability and its underlying regulatory networks in <i>M. oryzae</i> remain unclear. In this study, we investigated the oxidative effects of citral on <i>M. oryzae</i> and conducted transcriptomic and widely targeted metabolomic (WTM) analyses on the mycelia. The results showed that citral induced superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) activities but reduced glutathione S-transferase (GST) activity with 25% maximal effective concentration (EC₂₅) and 75% maximal effective concentration (EC₇₅). Importantly, citral at EC₇₅ reduced the activities of mitochondrial respiratory chain complex I, complex III and ATP content, while increasing the activity of mitochondrial respiratory chain complex II. In addition, citral triggered a burst of reactive oxygen species (ROS) and a loss of mitochondrial membrane potential (MMP) through the observation of fluorescence. Furthermore, RNA-seq analysis and metabolomics analysis identified a total of 466 differentially expression genes (DEGs) and 32 differential metabolites (DAMs) after the mycelia were treated with citral. The following multi-omics analysis revealed that the metabolic pathways centered on AsA, GSH and melatonin were obviously suppressed by citral, indicating a disrupted redox equilibrium in the cell. These findings provide further evidences supporting the antifungal activity of citral and offer new insights into the response of <i>M. oryzae</i> under oxidative stress induced by citral.