Methyl Jasmonate Activates the 2C Methyl-D-erithrytol 2,4-cyclodiphosphate Synthase Gene and Stimulates Tanshinone Accumulation in Salvia miltiorrhiza Solid Callus Cultures

Isolation of Salvia miltiorrhiza Kaurene Synthase-like (KSL) Gene Promoter and Its Regulation by Ethephon and Yeast Extract

The presented study describes the regulation of the promoter region of the Salvia miltiorrhiza kaurene synthase-like gene (SmKSL) by ethylene and yeast extract. The isolated fragment is 897 bp and is composed of a promoter (763 bp), 5'UTR (109 bp), and a short CDS (25 bp). The initial in silico analysis revealed the presence of numerous putative cis-active sites for trans-factors responding to different stress conditions. However, this study examines the influence of ethylene and yeast extract on SmKSL gene expression and tanshinone biosynthesis regulation. The results of 72h RT-PCR indicate an antagonistic interaction between ethylene, provided as ethephon (0.05, 0.10, 0.25, and 0.50 mM), and yeast extract (0.5%) on SmKSL gene expression in callus cultures of S. miltiorrhiza. A similar antagonistic effect was observed on total tanshinone concentration for up to 60 days. Ethylene provided as ethephon (0.05, 0.10, 0.25, and 0.50 mM) is a weak inducer of total tanshinone biosynthesis, increasing them only up to the maximum value of 0.67 ± 0.04 mg g^-1 DW (60-day induction with 0.50 mM ethephon). Among the tanshinones elicited by ethephon, cryptotanshinone (52.21%) dominates, followed by dihydrotanshinone (45.00%) and tanshinone IIA (3.79%). In contrast, the 0.5% yeast extract strongly increases the total tanshinone concentration up to a maximum value of 13.30 ± 1.09 mg g^-1 DW, observed after 50 days of induction. Yeast extract and ethylene appear to activate different fragments of the tanshinone biosynthesis route; hence the primary tanshinones induced by yeast extract were cryptotanshinone (81.42%), followed by dihydrotanshinone (17.06%) and tanshinone IIA (1.52%).

Effect of Stress Signals and Ib-rolB/C Overexpression on Secondary Metabolite Biosynthesis in Cell Cultures of Ipomoea batatas

Ipomoea batatas is a vital root crop and a source of caffeoylquinic acid derivatives (CQAs) with potential health-promoting benefits. As a naturally transgenic plant, I. batatas contains cellular T-DNA (cT-DNA) sequence homologs of the Agrobacterium rhizogenes open reading frame (ORF)14, ORF17n, rooting locus (Rol)B/RolC, ORF13, and ORF18/ORF17n of unknown function. This study aimed to evaluate the effect of abiotic stresses (temperature, ultraviolet, and light) and chemical elicitors (methyl jasmonate, salicylic acid, and sodium nitroprusside) on the biosynthesis of CQAs and cT-DNA gene expression in I. batatas cell culture as a model system. Among all the applied treatments, ultraviolet irradiation, methyl jasmonate, and salicylic acid caused the maximal accumulation of secondary compounds. We also discovered that I. batatas cT-DNA genes were not expressed in cell culture, and the studied conditions weakly affected their transcriptional levels. However, the Ib-rolB/C gene expressed under the strong 35S CaMV promoter increased the CQAs content by 1.5-1.9-fold. Overall, our results show that cT-DNA-encoded transgenes are not involved in stress- and chemical elicitor-induced CQAs accumulation in cell cultures of I. batatas. Nevertheless, overaccumulation of RolB/RolC transcripts potentiates the secondary metabolism of sweet potatoes through a currently unknown mechanism. Our study provides new insights into the molecular mechanisms linked with CQAs biosynthesis in cell culture of naturally transgenic food crops, i.e., sweet potato.