Transcriptomic and metabolomic analysis of Bacillus subtilis/sodium alginate coating-induced molecular responses in...

Citrus fruits are susceptible to abiotic stress after harvest, and their wounds often become primary sites of infection by pathogenic fungi such as Penicillium italicum (P. italicum), leading to severe quality deterioration and economic losses. Although previous studies have shown that a Bacillus subtilis/sodium alginate (SA) coating can effectively maintain the postharvest quality of pomelos, the underlying molecular mechanisms remain unclear. In light of this, this study investigated the effects of B. subtilis/SA coating on defense compounds and defense-related enzyme activities in post-harvest Wendan pomelos, as well as its potential mechanisms of action. The results indicated that, at the physiological level, the treatment group increased the activity of defense-related enzymes (PAL, POD, SOD, etc.) and antioxidant capacity, while promoting the accumulation of resistant metabolites (total phenols, flavonoids, lignin); furthermore, it significantly inhibited the formation of malondialdehyde (MDA). A combined transcriptomic and metabolomic analysis identified a total of 905 differentially expressed genes (DEGs) and 91 differentially accumulated metabolites (DAMs). GO and KEGG enrichment analyses revealed that this treatment primarily enhances fruit resistance through the biosynthesis pathways of phenylpropanoids and flavonoids. Key DEGs involved in plant resistance responses (PR genes, PAL and CHS genes, etc.) were significantly upregulated, consistent with the observed increases in enzyme activity and metabolite accumulation at the physiological level. Correlation analysis further revealed potential regulatory networks between PAL, CHS, coumaric acid, caffeic acid and catechins. The results indicate that the B. subtilis/SA coating primarily induces fruit resistance by activating the host's defense response at the wound site at both the transcriptional and metabolic levels. In conclusion, this study provides a theoretical basis for the molecular mechanisms of post-harvest protection of Wendan pomelo mediated by B. subtilis/SA coating treatment.