Molecular characterization of 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) in relation to aconite biosynthesis in Aconitum heterophyllum Wall ex Royle

Abstract

Aconitum heterophyllum (Rananculaceae) is the only nonpoisonous aconite acclaimed for its production of high-value diterpene alkaloids commonly known as aconites. These compounds are synthesized in the plant through two independent pathways: 2-C-methyl-d-erythritol-4-phosphate or non-mevalonate pathway and mevalonate pathway. It is reported that 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) is a key enzyme involved in the biosynthesis of diversity of terpenoids. Only a handful of enzymes implicated in the biosynthesis of terpenoids have been characterized and sequenced until now from the plant species. From the current study, HMGR from A. heterophyllum was isolated for the first time along with its tissue-specific expression. The isolated gene was nominated as AhHMGR with 1647 bps of ORF. The sequence was submitted to NCBI data base with accession submission ID 2088147. The 3-domain architecture of class I type of HMGR was obtained after modelling. Like other HMGRs, an active site with a cofactor along with the substrate-binding motifs was obtained. The real-time reverse transcription polymerase chain reaction results revealed differential expression levels in different plant parts. The transcript level was higher in rhizome, followed by stem, leaf and flower which were in corroboration with the accumulation of aconites as depicted through HPLC analysis. The results from our study can be exploited for future molecular intervention to alter the metabolic flux towards improvement of key active ingredient in this important medicinal plant.