Protecting tobacco plants from O3 injury by Bacillus velezensis with production of acetoin

Plant growth-promoting rhizobacteria (PGPRs) confer benefits to crops by producing volatile organic compounds (VOCs) to trigger induced systemic tolerance (IST). Here we show thatBacillus velezensisGJ11, a kind of PGPRs, produce VOCs such as 2,3-butanediol and acetoin to trigger IST and cause stomatal closure against O(3)injury in tobacco plants. Compared to 2,3-butanediol, acetoin was more effective on triggering IST against O(3)injury. Thebdh-knockout strain GJ11 Delta bdhwith a blocked metabolic pathway from acetoin to 2,3-butanediol produced more acetoin triggering stronger IST against O(3)injury than GJ11. Both acetoin and GJ11 Delta bdheffectively enhance the antioxidant enzymes activity (e.g. superoxide dismutase and catalases) that is favorable for scavenging the reactive oxygen species like H(2)O(2)in leaves after exposure to O-3. Consequently, less H(2)O(2)accumulation was observed, and reasonably less chlorophylls and proteins were damaged by H(2)O(2)in the tobacco leaves treated with acetoin or GJ11 Delta bdh. The field experiment also showed that both acetoin and GJ11 Delta bdhcould protect tobacco plants from O(3)injury after application by root-drench. This study provides new insights into the role of rhizobacterialB. velezensisand its volatile component of acetoin in triggering defense responses against stresses such as O(3)in plants.