Expression pattern of fifteen genes of non-mevalonate (MEP) and mevalonate (MVA) pathways in different tissues of endangered medicinal herb Picrorhiza kurroa with respect to picrosides content

Abstract

Picrorhiza kurroa, has become an endangered medicinal herb due to excessive utilization, therefore it necessitates the understanding of biology and molecular basis of major chemical constituents i.e. Picroside-I (P-I) and Picroside-II (P-II). Estimation of P-I and P-II in different tissues of P. kurroa showed that shoots contain only P-I whereas P-II is present only in roots. Differential conditions with varying concentrations of P-I (0-27 μg/mg) and P-II (0-4 μg/mg) were selected. Four genes of MEP pathway; DXPS, ISPD, ISPE, MECPS and one gene of MVA pathway PMK showed elevated levels of transcripts in shoots (57-166 folds) and stolons (5-15 folds) with P-I contents 0-27 μg/mg and 2.9-19.7 μg/mg, respectively. Further HDS and DXPR genes of MEP pathway showed higher expression ~9-12 folds in roots having P-II (0-4 μg/mg). The expression of ISPH and ISPE was also high ~5 folds in roots accumulating P-II. GDPS was the only gene with high transcript level in roots (9 folds) and shoots (20 folds). Differential biosynthesis and accumulation of picrosides would assist in regulating quality of plant material for herbal drug formulations.

Mining NGS transcriptomes for miRNAs and dissecting their role in regulating growth, development, and secondary metabolites production in different organs of a medicinal herb, Picrorhiza kurroa

“…Previous studies have shown that shoots grown in tissue culture at 25°C (PKS-25) contain negligible P-I, whereas shoots grown in tissue culture at 15°C (PKS-15) contain slight P-I content (6 lg/mg) (Sood and Chauhan 2010). On the other hand, field-grown shoots (PKSS) contain a considerable amount of P-I content (27 lg/mg) (Pandit et al 2013), which is a contrasting condition for analyzing picroside biosynthesis at molecular level. Spatio-temporal biosynthesis and accumulation of secondary metabolites is influenced by conditions of organ, tissue specificity, and developmental stages of the plant as reported in case of cell type-specific localization of protoberberine alkaloid in roots and rhizomes of T. flavum (Samanani et al 2005) and in Fagopyrum species (Gupta et al 2011).…”

Biosynthesis and therapeutic implications of iridoid glycosides from Picrorhiza genus: the road ahead

“…MEP pathway was discovered in 1990s (Rohmer et al 1993), that starts from the condensation of glyceraldehyde-3-phosphate and pyruvate to produce DXP as the first intermediate. The key evidence for the involvement of MVA and MEP pathways in biosynthesis of picrosides was provided by the gene expression analyses performed under differential conditions of picrosides accumulation in P. kurroa (Pandit et al 2013b). Moreover, the gene expression patterns vis-à-vis P-I content were also observed in P. kurroa shoots at different time intervals of plant growth at 15°C under tissue culture conditions.…”

An insight into conflux of metabolic traffic leading to picroside-I biosynthesis by tracking molecular time course changes in a medicinal herb, Picrorhiza kurroa

“…The selected genes encoded the enzymes of glycolysis (hexokinase, HK; pyruvate kinase, PK), TCA cycle (isocitrate dehydrogenase, ICDH; malate dehydrogenase, MDH), pentose phosphate pathway (glucose-6-phosphate dehydrogenase, G-6-PDH), shikimate/phenylpropanoid pathway (3-deoxy-D-arabinoheptulosonate 7-phosphate synthase, DAHPS; phenylalanine ammonia lyase, PAL), mevalonate pathway (hydroxymethylglutaryl-CoA reductase, HMGR) and nonmevalonate pathway (1-deoxy-D-xylulose-5-phosphate synthase, DXPS). In addition, the genes encoding the enzymes, 4-diphosphocytidyl-2C-methyl-D-erythritol synthase (ISPD) and phosphomevalonate kinase (PMK) were also selected which previously showed enhanced elevation vis-à-vis P-I content under different growth conditions of P. kurroa (Pandit et al 2013b). The gene coding geraniol synthase (GS) was also selected as it showed significant fold increase in shoots of P. kurroa exposed to 15°C as compared to 25°C (Gahlan et al 2012).…”

“…Finally, geraniol-10-hydroxylase (G-10-H) gene was chosen as it is one of the first two genes in P-I biosynthesis which was used as a bait to decipher the enzymes of seco-iridoid pathway in Catharanthus roseus (Miettinen et al 2014). The primers of mevalonate and non-mevalonate pathway genes (DXPS, ISPD, HMGR and PMK) were procured from Pandit et al (2013b) while glycolysis (HK, PK), TCA cycle (ICDH, MDH) and pentose phosphate pathway (G6PDH) were procured from Kumar et al (2015). The primers for rest of the selected genes were designed from transcriptomic sequences of P. kurroa by using Primer3 software.…”

“…Recently, in addition to the documentation of proposed biosynthetic pathway of picrosides , the major progress in P-I biosynthesis pertains to modulation in expression patterns of genes involved in the mevalonate, non-mevalonate and primary metabolic pathways vis-a-vis P-I content under different growth conditions of P. kurroa (Kumar et al 2015;Pandit et al 2013b;Singh et al 2013). Although these reports have given us valuable insights into P-I biosynthesis yet these remain silent in the absence of a specific trigger.…”