Proteomic insights of chitosan mediated inhibition of Fusarium oxysporum f. sp. cucumerinum.

Fusarium oxysporum f. sp. cucumerinum (FOC) infects cucumber plants, causing significant yield losses. Chitosan is a natural biodegradable compound that has antifungal properties. To understand the inhibitory mechanism of chitosan against FOC, a comprehensive proteomic study was carried out for the identification of chitosan responsive proteins (CRPs) from the mycelia of chitosan-treated FOC. Two-dimensional gel electrophoresis (2-DE) coupled with LC-MS/MS analysis led to the identification of 62 differentially abundant CRPs. Functional classification of these CRPs revealed that most proteins were involved in metabolism and defense. Gene Ontology analysis revealed that the majority of the proteins were assigned in proteolysis and hydrolase activity. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that among the biologically active pathways in chitosan-treated FOC mycelia, 'carbohydrate metabolism' was enriched for most of the proteins. This study gives a snapshot of the molecular basis of fungal inhibition by chitosan resulting in disease resistance in cucumber plants after inoculation with chitosan-treated FOC by explaining how chitosan restricted disease severity (i.e., down-regulating the plant cell wall degrading enzymes, FOC self-attack, hindering FOC structural and functional protein biosynthesis and DNA biosynthesis and affecting FOC transporter proteins). This study contributes to putting more weight on using the bioactive natural compound chitosan as an antifungal material instead of applying chemical fungicides in agriculture. SIGNIFICANCE: Chitosan has been used as one of the safe and effective alternatives to fungicides in controlling cucumber vascular wilt disease caused by Fusarium oxysporum f. sp. cucumerinum (FOC) that is responsible for severe production losses. Chitosan application showed a significant decrease in wilt disease severity compared to chitosan untreated FOC and showed an efficiency of 91.7% in reducing pathogenicity. A comprehensive proteomic investigation of chitosan-responsive proteins (CRPs) from the mycelia of chitosan-treated FOC was carried out in order to better understand the inhibitory mechanism of chitosan against FOC which led us to identify 62 differentially expressed CRPs. Our proteomic study revealed CRPs in FOC involved in a variety of functions, including disease inhibition in cucumber. This study depicts what happens inside the fungus following treatment with chitosan and how chitosan played the role of the maestro in influencing the synthesis of proteins responsible for the virulence of FOC and their respective pathways, rendering FOC unable to infect the cucumber plant and lose its pathogenic potential to cause wilt disease. The efficiency of chitosan in inhibiting certain proteins or specific pathways of FOC gives a golden opportunity in controlling vascular wilt, so we highly recommend applying chitosan in disease management under greenhouse conditions or in the open field.