Exogenous Phytohormone Activators Enhance Rice Resistance to Brown Planthoppers by Boosting the Phenylpropanoid Pathway under Elevated CO 2

Studies indicate that elevated CO2 (eCO2) exacerbates brown planthopper (BPH, Nilaparvata lugens) damage to rice compared to ambient CO2 (aCO2), highlighting the need for enhanced pest resistance strategies under climate change. The phenylpropanoid pathway, activated by phytohormones, synthesizes defense compounds in plants. This study investigated exogenous abscisic acid (ABA) and strigolactone analogue (GR24) treatments on rice defense against BPH under aCO2 and eCO2. Results showed that ABA and GR24 suppressed BPH feeding and survival, particularly under eCO2, while activating the phenylpropanoid pathway and increasing furocoumarin accumulation─more pronounced under eCO2 than aCO2. These furocoumarins exhibited antifeeding effects and reduced BPH survival. Additionally, enzyme assays and molecular docking revealed enhanced detoxification activity in BPH feeding on treated rice or furocoumarin-laced diets under eCO2. These findings demonstrate that ABA and GR24 enhance rice resistance to BPH by activating phenylpropanoid metabolism under eCO2, providing a mechanistic basis for climate-resilient pest management strategies.