High light promotes salicylic acid–dependent diterpenoid lactone biosynthesis in Andrographis paniculate

The medicinal plant Andrographis paniculata produces bioactive compounds, including andrographolide and its derivatives, with diverse clinical applications. However, the mechanisms regulating andrographolide biosynthesis remain unclear. We show that high-light conditions enhance the accumulation of andrographolide and its derivatives in A. paniculata . Integrated metabolomic and transcriptomic analyses confirmed high-light–induced andrographolide biosynthesis. High-light treatment also increased salicylic acid (SA) and SA glucoside levels. Exogenous SA further promoted the accumulation of andrographolide and its derivatives under both growth light and high-light conditions. Mechanistically, the light signaling factor PHYTOCHROME-INTERACTING FACTOR 1 (ApPIF1) activated transcription of the geranylgeranyl diphosphate synthase gene ( ApGGPPS2 ), while the SA signaling factor ApWRKY40 activated transcription of the copalyl diphosphate synthase gene ApCPS2 . Both ApGGPPS2 and ApCPS2 encode key enzymes in andrographolide biosynthesis. Silencing ApPIF1 or ApWRKY40 significantly reduced andrographolide levels. Moreover, ApPIF1 physically interacted with ApWRKY40, indicating that this regulatory module integrates high-light and SA signals to control andrographolide metabolism. Our findings reveal how light intensity influences andrographolide biosynthesis in A. paniculata and provide new insights into light-induced metabolite accumulation. Geranylgeranyl diphosphate synthase ( GGPPS ), Copalyl diphosphate synthase ( CPS ), and UDP-glucosyltransferase ( UGT ).