Molecular cloning and characterization of Triterpenoid Biosynthetic Pathway Gene HMGS in Centella asiatica (Linn.)

The flux of isoprenoids and the total accumulation of triterpenoid saponins known as centellosides in C. asiatica are controlled by the key genes of the Mevalonate pathway (MVA). These genes were reported to have positive regulation of the pathway in providing isoprenoid moieties. Though, some information is available on the pathway and secondary metabolites. However, most of the pathway steps are not characterized functionally.

For the study, full-length pathway gene Hydroxymethyl glutaryl-CoA-synthase (CaHMGS; GenBank accession number: MZ997833), was isolated from previously annotated transcriptome data of Centella asiatica leaves. HMGS has been successfully cloned and heterologously expressed in bacteria E. coli strain DH5α. The cloned gene has been sequenced and further characterized through in silico studies by different bioinformatics tools. Also, the gene sequences have been submitted in NCBI. In silico studies of isolated gene sequence revealed the nature, characteristics of genes. The ORF of HMGS is 1449 bp encoding 482 amino acids. Predicted molecular weight (MW) of HMGS was 48.09 kDa and theoretical pI was 5.97. Blast results and Multiple sequence alignments of the gene showing the similarity with HMGS of other plants of their respective families. The Molecular Evolutionary Genetic Analysis (MEGA) version 10.1.6 was used to construct a phylogenetic tree. Differential tissue-specific expression of different plant parts was also checked. Tissue expression patterns unveiled that the highest expression level of the CaHMGS had been seen in the roots and lowest in the node of the plant. Functional complementation experiment of the CaHMGS in Saccharomyces cerevisiae wild strain YSC1021 and haploid strain YSC1021 which lack HMGS protein confirmed that the CaHMGS gene encodes functional CaHMGS that catalyzed the biosynthesis of mevalonate in yeast.

The gene was reported, cloned and characterized first time in Centella asiatica. Understanding this biosynthetic pathway gene will further help in the improvement of plants for enhanced secondary metabolites production.