Abstract
Penicillium digitatum is the most severe pathogen that infects citrus fruits during storage. It can cause fruit rot and bring significant economic losses. The continuous use of fungicides has resulted in the emergence of drug-resistant strains. Consequently, there is a need to develop naturally and efficiently antifungal fungicides. Natural antimicrobial agents such as clove oil, cinnamon oil, and thyme oil can be extracted from different plant parts. They exhibited broad-spectrum antimicrobial properties and have great potential in the food industry. Here, we exploit a novel cinnamaldehyde (CA), eugenol (EUG), or carvacrol (CAR) combination antifungal therapy and formulate it into nanoemulsion form to overcome lower solubility and instability of essential oil. In this study, the antifungal activity evaluation and transcriptional profile of Penicillium digitatum exposed to compound nanoemulsion were evaluated. Results showed that compound nanoemulsion had a striking inhibitory effect on P. digitatum in a dose-dependent manner. According to RNA-seq analysis, there were 2,169 differentially expressed genes (DEGs) between control and nanoemulsion-treated samples, including 1,028 downregulated and 1,141 upregulated genes. Gene Ontology (GO) analysis indicated that the DEGs were mainly involved in intracellular organelle parts of cell component: cellular respiration, proton transmembrane transport of biological process, and guanyl nucleotide-binding molecular function. KEGG analysis revealed that metabolic pathway, biosynthesis of secondary metabolites, and glyoxylate and dicarboxylate metabolism were the most highly enriched pathways for these DEGs. Taken together, we can conclude the promising antifungal activity of nanoemulsion with multiple action sites against P. digitatum. These outcomes would deepen our knowledge of the inhibitory mechanism from molecular aspects and exploit naturally, efficiently, and harmlessly antifungal agents in the citrus postharvest industry.
Highlights
During the postharvest, handling, and transportation process, citrus usually suffers significant losses
Carvacrol has been demonstrated to have an antibacterial efficiency against Listeria monocytogenes and Escherichia coli [12]; eugenol has an antifungal activity against Cryptococcus gattii and C. neoformans [13]
KEGG enrichment analysis showed that most differentially expressed genes (DEGs) were enriched in the metabolic pathway, there were 144 down-regulated DEGs and 72 up-regulated DEGs respectively, indicating that the nanoemulsion inhibited the growth of P. digitatum by reducing its metabolic level
Summary
During the postharvest, handling, and transportation process, citrus usually suffers significant losses. Related studies show that citrus postharvest rot is mainly green mold caused by P. digitatum, accounting for more than 80% of the total crop losses [1]. A volatile aromatic compound, can be extracted from different parts of the plant [8]. Cinnamaldehyde and eugenol are the main components of cinnamon essential oil and clove oil, respectively. Carvacrol was found in the thyme oil or oregano oil and has been reported to possess antimicrobial activities [9,10,11]. Carvacrol has been demonstrated to have an antibacterial efficiency against Listeria monocytogenes and Escherichia coli [12]; eugenol has an antifungal activity against Cryptococcus gattii and C. neoformans [13]
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