Endophytic Bacterium-Triggered Reactive Oxygen Species Directly Increase Oxygenous Sesquiterpenoid Content and Diversity in Atractylodes lancea
ABSTRACTOxygenous terpenoids are active components of many medicinal plants. However, current studies that have focused on enzymatic oxidation reactions cannot comprehensively clarify the mechanisms of oxygenous terpenoid synthesis and diversity. This study shows that an endophytic bacterium can trigger the generation of reactive oxygen species (ROS) that directly increase oxygenous sesquiterpenoid content and diversity inAtractylodes lancea.A. lanceais a famous but endangered Chinese medicinal plant that contains abundant oxygenous sesquiterpenoids. Geo-authenticA. lanceaproduces a wider range and a greater abundance of oxygenous sesquiterpenoids than the cultivated herb. Our previous studies have shown the mechanisms behind endophytic promotion of the production of sesquiterpenoid hydrocarbon scaffolds; however, how endophytes promote the formation of oxygenous sesquiterpenoids and their diversity is unclear. After colonization byPseudomonas fluorescensALEB7B, oxidative burst and oxygenous sesquiterpenoid accumulation inA. lanceaoccur synchronously. Treatment with exogenous hydrogen peroxide (H2O2) or singlet oxygen induces oxidative burst and promotes oxygenous sesquiterpenoid accumulationin planta. Conversely, pretreatment of plantlets with the ROS scavenger ascorbic acid significantly inhibits the oxidative burst and oxygenous sesquiterpenoid accumulation induced byP. fluorescensALEB7B. Furtherin vitrooxidation experiments show that several oxygenous sesquiterpenoids can be obtained from direct oxidation caused by H2O2or singlet oxygen. In summary, this study demonstrates that endophytic bacterium-triggered ROS can directly oxidize oxygen-free sesquiterpenoids and increase the oxygenous sesquiterpenoid content and diversity inA. lancea, providing a novel explanation of the mechanisms of oxygenous terpenoid synthesisin plantaand an essential complementarity to enzymatic oxidation reactions.