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, <i>Nilaparvata lugens</i>) 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.