Stress-Responsive Alternative Sigma Factor SigB Plays a Positive Role in the Antifungal Proficiency of .

Different species with PGPR (plant growth-promoting rhizobacterium) activity produce potent biofungicides and stimulate plant defense responses against phytopathogenic fungi. However, very little is known about how these PGPRs recognize phytopathogens and exhibit the antifungal response. Here, we report the antagonistic interaction between and the phytopathogenic fungus We demonstrate that this bacterial-fungal interaction triggers the induction of the SigB transcription factor, the master regulator of stress adaptation. Dual-growth experiments performed with live or dead mycelia or culture supernatants of showed that SigB was activated and required for the biocontrol of fungal growth. Mutations in the different regulatory pathways of SigB activation in the isogenic background revealed that only the energy-related RsbP-dependent arm of SigB activation was responsible for specific fungal detection and triggering the antagonistic response. The activation of SigB increased the expression of the operon responsible for the production of the antimicrobial cyclic lipopeptide surfactin (the operon). SigB-deficient cultures produced decreased amounts of surfactin, and cultures defective in surfactin production (Δ) were unable to control the growth of experiments of seed germination efficiency and early plant growth inhibition in the presence of confirmed the physiological importance of SigB activity for plant bioprotection. Biological control using beneficial bacteria (PGPRs) represents an attractive and environment-friendly alternative to pesticides for controlling plant diseases. Different PGPR species produce potent biofungicides and stimulate plant defense responses against phytopathogenic fungi. However, very little is known about how PGPRs recognize phytopathogens and process the antifungal response. Here, we report how triggers the induction of the stress-responsive sigma B transcription factor and the synthesis of the lipopeptide surfactin to fight the phytopathogen. Our findings show the participation of the stress-responsive regulon of PGPR in the detection and biocontrol of a phytopathogenic fungus of agronomic impact.