Inhibition of target of rapamycin signaling suppresses growth and andrographolide biosynthesis in Andrographis paniculata

The target of rapamycin (TOR) is a central regulator of growth-defense trade-offs in plants; however, its role in secondary metabolite biosynthesis in medicinal plants remains unclear. This study investigated the metabolic and transcriptional mechanisms by which TOR signaling modulates both plant growth and andrographolide accumulation in Andrographis paniculata, employing the TOR inhibitor AZD-8055 (AZD). We found that treatment with 5 µmol·L− 1 AZD significantly suppressed plant growth and reduced andrographolide content. Transcriptomic analysis showed that AZD treatment upregulated pathways involved in plant–pathogen interactions, carbon metabolism, and MAPK signaling, while downregulating pathways related to fatty acid elongation, plant hormone signaling, diterpenoid biosynthesis, photosynthesis, and tryptophan metabolism. Moreover, TOR inhibition disrupted the balance between carbon and nitrogen metabolites. Notably, inhibition of TOR signaling influenced the biosynthesis, activation, and signaling pathways of defensive phytohormones, including abscisic acid (ABA), jasmonic acid (JA), salicylic acid (SA), and auxin. These phytohormones likely mediate the TOR-dependent coordination of growth and andrographolide biosynthesis in A. paniculata. Collectively, the findings suggest that TOR is indispensable for integrating plant growth with andrographolide biosynthesis, with ABA, JA, SA, and auxin signaling pathways serving as critical mediators in this regulatory process. This study advances our understanding of the trade-offs between growth and secondary metabolite biosynthesis in A. paniculata.