Transcriptome analysis reveals key genes involved in luteolin-induced resistance against sour rot in navel orange fruit

Abstract Sour rot significantly contributes to postharvest decay in citrus fruit. Luteolin has been utilized as a preservative in fruit, but its effectiveness and mechanisms against sour rot in citrus fruit are not well understood. In this research, luteolin was utilized to inhibit the primary sour rot fungal pathogen, Geotrichum citri-aurantii, in navel orange fruit. Luteolin treatment with 10-fold inhibitory concentration reduced lesion diameter by up to 29.38% and disease incidence by 18.18%. Additionally, luteolin treatment lowered malondialdehyde and hydrogen peroxide contents, enhanced total phenolic and flavonoid contents, maintained elevated protopectin and cellulose levels, and increased the activities of resistance-related enzymes in navel orange peel. Transcriptome analysis revealed that 241 genes exhibited differential expression between control and luteolin-treated navel peel at 3 d post-inoculation. Gene ontology analysis showed enrichment of differentially expressed genes in oxidoreductase activity, antioxidant activity, and cell wall function. Specifically, CsMUTE and CsGRXS9 were upregulated, whereas CsPE2, CsPGL3, and CsRbohD were downregulated following luteolin treatment. Through correlation analysis, strong associations were established between the CsMUTE transcription factor and structural genes. Furthermore, the phenotypes of CsMUTE transgenic citrus peel and tomato fruit suggest that CsMUTE is involved in providing resistance to Geotrichum citri-aurantii. These findings collectively show that luteolin treatment regulates sour rot by directly inhibiting fungi and triggering citrus fruit defense mechanisms. This offers new perspectives and practical strategies for environmentally friendly citrus fruit preservation.