Characterization and expression of two cDNA encoding 3-Hydroxy-3-methylglutaryl coenzyme A reductase isoforms in coffee (Coffea arabica L.)

Low-Copy Genes in Terpenoid Metabolism: The Evolution and Expression of MVK and DXR Genes in Angiosperms

Terpenoids are a diverse class of metabolites that impact plant metabolism in response to environmental cues. They are synthesized either via a predominantly cytosolic (MVA) pathway or a plastidic pathway (MEP). In Arabidopsis, several enzymes from the MVA and MEP pathways are encoded by gene families, excluding MVK and DXR, which are single-copy genes. In this study, we assess the diversity, evolution and expression of DXR and MVK genes in selected angiosperms and Coffea arabica in particular. Evolutionary analysis revealed that DXR and MVK underwent purifying selection, but the selection effect for DXR was stronger than it was for MVK. Digital gene expression (DGE) profile analysis of six species revealed that expression levels of MVK in flowers and roots were high, whereas for DXR peak values were observed in leaves. In C. arabica, both genes were highly expressed in flowers, and CaDXR was upregulated in response to methyl jasmonate. C. arabica DGE data were validated by assessing gene expression in selected organs, and by plants treated with hexanoic acid (Hx) using RT-qPCR. MVK expression was upregulated in roots treated with Hx. CaDXR was downregulated in leaves by Hx treatment in a genotype-specific manner, indicating a differential response to priming.

Isolation, characterization and in silico analysis of 3-Hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR) gene from Andrographis paniculata (Burm. f) Nees

3-Hydroxy-3-methylglutaryl-coenzymeA reductase (HMGR), the first rate-limiting enzyme of Mevalonate (MVA) pathway was isolated from Andrographis paniculata (ApHMGR) and expressed in bacterial cells. Full length ApHMGR (1937 bp) was submitted to NCBI with accession number MG271748.1. The open reading frame (ORF) was flanked by a 31-bp 5'-UTR, 118-bp 3'-UTR and ApHMGR contained a 1787 bp ORF encoding protein of 595 amino acids. ApHMGR protein was approximately 64 kDa, with isoelectric point of 5.75. Isolated ApHMGR was cloned into pET102 vector and expressed in E. coli BL21 (DE 3) cells, and characterized by SDS-PAGE. HPLC analysis for andrographolide content in leaf, stem and root of A. paniculata revealed highest in leaf tissue. The expression patterns of ApHMGR in different plant tissues using qRT-PCR revealed high in root tissue correlating with HPLC data. Three dimensional (3D) structural model of ApHMGR displayed 90% of the amino acids in most favored regions of the Ramachandran plot with 93% overall quality factor. ApHMGR was highly conserved with plant specific N-terminal membrane domains and C-terminal catalytic regions. Phylogenetic analysis showed A. paniculata sharing common ancestor with Handroanthus impetiginosus. 3D model of ApHMGR was screened for the interaction with substrates NADPH, HMG CoA and inhibitor using Auto Dock Vina. In silico analysis revealed that full length ApHMGR had extensive similarities to other plant HMGRs. The present communication reports the isolation of full length HMGR from A. paniculata, its heterologous expression in bacterial cells and in silico structural and functional characterization providing valuable genomic information for future molecular interventions.

Characterization and functional analysis of two novel 3-hydroxy-3-methylglutaryl-coenzyme A reductase genes (GbHMGR2 and GbHMGR3) from Ginkgo biloba

Terpene trilactones (TTLs) are the main secondary metabolites of Ginkgo biloba. As one of the rate-limiting enzymes in the mevalonic acid (MVA) pathway of TTL biosynthesis, 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR) catalyzes the 3-hydroxy-3-methylglutaryl coenzyme A to form MVA. In this study, two cDNA sequences of HMGR genes, namely, GbHMGR2 and GbHMGR3, were cloned from G. biloba. The protein sequences of GbHMGR2 and GbHMGR3, which contain several functional domains, were analyzed. Regulatory elements related to light, hormone, and stress response were detected in the promoter regions of GbHMGR2 and GbHMGR3. The catalytic activity of these genes was verified by a functional complement experiment in yeast. Quantitative real-time PCR (qRT-PCR) showed the distinct expression patterns of the two genes in different organs. The TTL contents in the organs were detected by high-performance liquid chromatography- evaporative light scattering detector. GbHMGR2 and GbHMGR3 were responded to cold, dark, methyl jasmonate (MJ), abscisic acid (ABA), salicylic acid (SA), and ethephon (Eth) treatments. The TTL contents were also regulated by cold, dark, MJ, ABA, SA, and Eth treatment. In conclusion, GbHMGR2 and GbHMGR3 may participate in the MVA pathway of TTL biosynthesis.

Recent advances in steroidal saponins biosynthesis and in vitro production

Steroidal saponins exhibited numerous pharmacological activities due to the modification of their backbone by different cytochrome P450s (P450) and UDP glycosyltransferases (UGTs). Plant-derived steroidal saponins are not sufficient for utilizing them for commercial purpose so in vitro production of saponin by tissue culture, root culture, embryo culture, etc, is necessary for its large-scale production. Saponin glycosides are the important class of plant secondary metabolites, which consists of either steroidal or terpenoidal backbone. Due to the existence of a wide range of medicinal properties, saponin glycosides are pharmacologically very important. This review is focused on important medicinal properties of steroidal saponin, its occurrence, and biosynthesis. In addition to this, some recently identified plants containing steroidal saponins in different parts were summarized. The high throughput transcriptome sequencing approach elaborates our understanding related to the secondary metabolic pathway and its regulation even in the absence of adequate genomic information of non-model plants. The aim of this review is to encapsulate the information related to applications of steroidal saponin and its biosynthetic enzymes specially P450s and UGTs that are involved at later stage modifications of saponin backbone. Lastly, we discussed the in vitro production of steroidal saponin as the plant-based production of saponin is time-consuming and yield a limited amount of saponins. A large amount of plant material has been used to increase the production of steroidal saponin by employing in vitro culture technique, which has received a lot of attention in past two decades and provides a way to conserve medicinal plants as well as to escape them for being endangered.