Plant growth-promoting rhizobacteria (PGPRs) confer benefits to crops by producing volatile organic compounds (VOCs) to trigger induced systemic tolerance (IST). Here we show that
Bacillus velezensis GJ11, 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. The
bdh-knockout strain GJ11Δ
bdh with 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 GJ11Δ
bdh effectively enhance the antioxidant enzymes activity (e.g. superoxide dismutase and catalases) that is favorable for scavenging the reactive oxygen species like H
2O
2 in leaves after exposure to O
3. Consequently, less H
2O
2 accumulation was observed, and reasonably less chlorophylls and proteins were damaged by H
2O
2 in the tobacco leaves treated with acetoin or GJ11Δ
bdh. The field experiment also showed that both acetoin and GJ11Δ
bdh could protect tobacco plants from O
3 injury after application by root-drench. This study provides new insights into the role of rhizobacterial
B. velezensis and its volatile component of acetoin in triggering defense responses against stresses such as O
3 in plants.
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