Manipulation of DXP pathway for andrographolide production in callus cultures of Andrographis paniculata

Main conclusion Greening of in vitro callus cultures and andrographolide over-accumulation was achieved by manipulating light exposure and media composition, when the biosynthetic cascade was channeled through the DXP pathway. Andrographolide, the primary biologically active compound of Andrographis paniculata, is produced through coordinated action of two pathways, the classical cytosolic mevalonate pathway and the alternative plastidial non-mevalonate pathway (Deoxy-xylulose Phosphate pathway). In vitro callus cultures of A. paniculata are useful sources of production, as well as, manipulation of andrographolide, and the present study was designed to explore the strategy of pathway inhibition for its overproduction. When the cytosolic mevalonate pathway blocker, lovastatin, was applied to callus cultures of A. paniculata, andrographolide production was enhanced in comparison to untreated control. In contrast, treatment of the callus tissue with the DXP-pathway blocker, fosmidomycin, led to depletion in andrographolide production. The present study also showed that silver nitrate, a potent elicitor of andrographolide production in in vitro callus culture, when added in combination with the pathway inhibitors resulted in alterations in andrographolide production. The highest andrographolide production was obtained in callus treated with a combination of silver nitrate and lovastatin, indicating a predominant role of the plastidial DXP pathway in andrographolide biosynthesis. A positive co-relation with chlorophyll content and andrographolide production in in vitro callus cultures (untreated and treated) observed also supported the above assumption. It could be inferred from this study that greening of callus tissue through organellar organization was a potent strategy for enhancing andrographolide accumulation in callus tissues of A. paniculata.