Postharvest biological control of Botrytis cinerea and the mechanisms underlying the induction of disease resistance in grapes by Lactobacillus plantarum CM-3

Abstract

Biological control by microbial antagonists has been proposed as a viable strategy for the control of postharvest diseases in fruit. In the present study, biocontrol efficacy of the bacterial antagonist Lactobacillus plantarum CM-3 against gray mold infection on harvested grapes was documented along with the underlying physiological and molecular mechanisms responsible for biocontrol activity. In this regard, a transcriptomic analysis of the response of grapes to L. plantarum CM3 was conducted. Results indicated that L. plantarum CM-3 significantly decreased the level of natural postharvest decay in grapes without causing any adverse effects on quality traits. Treatment of grapes with L. plantarum CM-3 (1 × 109 CFU mL−1) resulted in a 55 % reduction in disease incidence caused by Botrytis cinerea. Meanwhile, L. plantarum CM-3 enhanced the activity of several enzymes in grapes that are closely associated with defense, including POD, PPO, CAT, APX, PAL, and GLU. RNA-seq analysis indicated extensive changes in the gene expression profile of grape berries in response to being treated with L. plantarum CM-3. In total, 1,327 differentially expressed genes (DEGs) were identified, among which 78.1 % (1,037) were upregulated and 21.9 % (290) were downregulated. Numerous pathways were strongly influenced by the L. plantarum CM-3 treatment, including signal perception and transduction, maintenance of reactive oxygen species (ROS) homeostasis, transcriptional and post-transcriptional regulation, primary metabolic pathways, and secondary metabolism. Additionally, the expression of 22 DEGs linked to enhancing disease resistance was analyzed by RT-qPCR and their expression levels were found to well correspond with the results obtained in the analysis of the RNA-seq data. Our data indicate that L. plantarum CM-3 can enhance host resistance by altering the expression of defense genes and their corresponding proteins, including PR1, WRKY33, WRKY22, PTI6 and peroxidase isoenzyme. Collectively, results of our study indicate that L. plantarum CM-3 treatment enhances the disease resistance of harvested grapes through a comprehensive and complex regulatory network. These findings provide new information on the molecular mechanism responsible for the enhancement of host disease resistance in grapes by L. plantarum CM-3. It also demonstrates a biocontrol strategy that can be used to elicit defense responses in fruit against fungal pathogens.