Bacillus amyloliquefaciens WS-10 induces systemic resistance in flue-cured tobacco plants against bacterial wilt disease

Bacterial wilt caused by soilborne plant pathogenic bacterium Ralstonia solanacearum seriously threaten the flue-cured tobacco production. Biological control has been implicated as an effective and safe method to suppress plant disease. Previously it is proved that Bacillus amyloliquefaciens WS-10, as a biocontrol agent significantly suppressed the incidence of bacterial wilt disease on flue-cured tobacco plants by successful colonization with the host and shifting the rhizosphere microbiome towards a healthy state. This study aimed to explore the activities of defense-related antioxidant enzymes and transcriptional response in the roots of flue-cured tobacco plants to bacterial wilt pathogen and B. amyloliquefaciens WS-10 to unravel the underlying biocontrol mechanism of B. amyloliquefaciens WS-10 against tobacco bacterial disease. The experiment was performed under two conditions T1 (treatment of R. solanacearum WS-001) and T2 (combined application of R. solanacearum WS-001 + B. amyloliquefaciens WS-10). Root samples were collected from each treatment at three time points before inoculation (at 0 h) as control and after inoculation (at 24 h and 72 h) for the analysis of activities of defense-related antioxidant enzymes and RNA-sequencing. Results demonstrated that the activities of defense-related antioxidant enzymes (SOD, POD, PPO, and PAL) significantly increased in the roots of T2 compared with T1 after 72 h of post inoculation (hpi). Further transcriptome analysis revealed in total 12,198 (4771 up- and 7427 down-regulated) differentially expressed genes (DEGs) in groupwise comparisons after 0, 24, and 72 hpi. B. amyloliquefaciens WS-10 activated the phenylpropanoid biosynthesis pathway and increased the expression of genes related to antioxidant enzymes, secondary metabolites, and lignin biosynthesis and involved in the jasmonic acid/ethylene plant disease resistance pathways. It is concluded that B. amyloliquefaciens WS-10 induces the systemic resistance in flue-cured tobacco plants against bacterial wilt infection by enhancing the plant defense and activities of antioxidants enzymes, activation of phenylpropanoid biosynthesis pathway, and reinforcement of the plant cell wall.