RNAi Mediated Silencing of Gene Encoding 1-Deoxy-D-Xylulose-5-Phosphate Reductoisomerase (DXR) in <i>Centella asiatica</i>

Abstract

Centella asiatica (L.) is one of the most valuable medicinal plants since preh istoric times. The pharmaceutical importance of this herb is due to the accumulation of large quantities of pentacyclic triterpenoid saponins, collectively known as centelloids synthesized by the isoprenoid biosynthesis path way. Biosynthesis of triterpenoid in the plants proceeds via either of the tw o pathways, viz. Mevalonate (MVA) pathway (in the cytosol) or 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway (in plastid). In Centella , the pathway leading to the accumulation of triterpenoid is still not known or elucidated. Thus, to know whether the MVA or MEP pathway or a cross-talk between the pathway leads to the biosynthesis of triterpenoid, silencing the key regulatory gene using RNAi tool, of each of the pathway and then analyze a metabolite is an efficient approach. The key regulatory enzyme of the MVA pathway i.e . 3- Hydroxy -3- methylglutaryl-coenzyme A reductase ( HMGR ) has already been successfully silenced using RNAi tool [1] . In the present study, the 1- deoxy-D-xylulose -5- phosphate reductoisomerase ( DXR ) a key regulatory enzyme in MEP pathway is silenced. The RNAi- DXR construct in pHANNIBAL vector was cloned into a binary vector pART27 and subsequently transformed into Agrobacterium strain AGL1. The transient analysis of the RNAi- CaDXR using semi-quantitative RT-PCR confirmed the silencing of the endogenous DXR gene in Nicotiana and further confirmed in Centella asiatica . The present study is the first step aimed to delineate the MEP pathway using RNAi silencing approach to elucidate its role in the accumulation of triterpenoid in this important medicinal plant.