Andrographolide (AD) is the time-honoured pharmacologically active constituent of the traditionally renowned medicinal plant-Andrographis paniculata. Advancements in the target-oriented drug discovery process have further unravelled the immense therapeutic credibility of another unique molecule-neoandrographolide (NAD). The escalated market demand of these anti-cancer diterpenes is increasingly facing unrelenting hurdles of demand and supply disparity, attributable to their limited yield. Callus and adventitious root cultures were generated to explore their biosynthetic potentials which first time revealed NAD production along with AD. Optimization of the types and concentrations of auxins along with media form and cultivation time led to the successful tuning towards establishing adventitious roots as a superior production alternative for both AD/NAD. Supplementation of IBA to the NAA + Kn-containing MS medium boosted the overall growth and AD/NAD synthesis in the adventitious roots. Compared to control leaves, the adventitious root exhibited about 2.61- and 8.8-fold higher contents of AD and NAD, respectively. The qRT-PCR involving nine key pathway genes was studied, which revealed upregulation of GGPS1 and HMGR1/2 genes and downregulation of DXS1/2 and HDR1/2 genes in the adventitious root as compared to that in the control leaves. Such observations highlight that in vitro cultures can serve as efficient production alternatives for AD/NAD as the cytosolic genes (HMGR1/2 of MVA pathway) are competent enough to take over from the plastidial genes (DXS1/2 and HDR1/2 of MEP pathway), provided the accredited first branch-point regulatory gene (GGPS) expression and the culture requirements are optimally fulfilled.
Keywords: Adventitious roots; Andrographis paniculata; Andrographolide; Biosynthetic pathway genes; Neoandrographolide; qRT-PCR.