Enhanced Production of Phenolic Compounds in Compact Callus Aggregate Suspension Cultures of Rhodiola imbricata Edgew

Comparative transcriptome and tissue-specific expression analysis of genes reveal tissue-cultured plants as an alternative source for phenylethanoids and phenylpropanoids in Rhodiola imbricata (Edgew.)

Rhodiola imbricata (Crassulaceae) is a traditional trans-Himalayan endangered medicinal herb with immense therapeutic applications. Over the years, over-exploitation, un-managed harvesting, and lack of captive cultivation procedures persuaded threat to its wild habitat. Plant tissue culture and RNA-Seq-based molecular bioprospection of key regulatory genes aid the understanding of molecular dynamics involved in specialized metabolites (phenylethanoids and phenylpropanoids) biosynthesis and its sustainable production. Hence, comparative transcriptomic analysis was performed using leaf and root tissues from the wild and tissue-cultured plants, revealing tissue-specific production of salidroside and rosavin. The transcriptome profiling resulted in 345 million high-quality reads yielding 92,380 unique transcripts with an N₅₀ of 1260 bp. Tissue-specific gene expression analysis revealed that both phenylethanoids and phenylpropanoids biosynthesis are predominantly associated with the shikimate pathway. In addition to RNA-Seq data, the downstream biosynthesis pathways genes viz., phospho-2-dehydro-3-deoxyheptonate aldolase (DAHPS), 3-dehydroquinate synthase (DHQS), shikimate kinase (SK), chorismate mutase (CM), arogenate dehydrogenase (TYRAAT), aromatic-L-amino-acid decarboxylase (TDC), phenylalanine ammonia-lyase (PAL), 4-coumarate-CoA ligase (4-CL), cinnamoyl-CoA reductase (CCR), and cinnamyl alcohol dehydrogenase (CAD) showed higher expression pattern in wild plant tissues compared to tissue-cultured plants. The transcript fold expression determined by RT-qPCR results followed similar patterns as those observed in RNA-seq and targeted metabolite profiling data. Salidroside and rosavin content in wild plants exhibited 2.40 fold and 1.77 fold increase accumulation compared to the tissue-cultured plant. The present investigation explained the tissue and condition-specific significant differences between the expression of proposed biosynthetic pathway genes and salidroside and rosavin content. Additionally, NAC, bHLH, and ARF were the most abundant transcription factor families found in the transcriptomic analysis of R. imbricata. The generated transcriptome dataset provides a valuable gene(s)/transcription factors hub that can be used for the sustainable production of salidroside and rosavin in R. imbricata under tissue culture conditions.

Enhanced Production of Phenylethanoids Mediated Through Synergistic Approach of Precursor Feeding and Light Regime in Cell Suspension Culture of Rhodiola imbricata (Edgew.)

Precursor feeding is a potential strategy for increasing specialized metabolite production in plant cell culture systems. In the present study, cell suspension cultures were developed and subsequently evaluated for precursor feeding investigations. Cell suspension cultures were established in Murashige and Skoog (MS) medium containing 0.5 mg/L thidiazuron (TDZ) + 1 mg/L α-naphthalene acetic acid (NAA). The growth biomass and metabolite pattern were analyzed to identify specific culture days required for prolific biomass production. The maximum cell dry weight (DW) was observed in leaf cell suspension (1.22 g/100 mL) and root cell suspension culture (1.12 g/100 mL) on day 21. Afterward, the effect of precursor concentrations (tyrosol; 0.5, 1, 2, and 3 mM) along with two light regimes, photoperiod (16L/8D h, 70 µmol/m²/s) and dark (24 h), was evaluated for cell growth and metabolite accumulation. The results revealed that leaf cell suspension treated with 3 mM tyrosol concentration detected maximum salidroside content (26.05 mg/g DW) on day 15, incubated under photoperiod (16L/8D h) condition. Similarly, under photoperiod (16L/8D h), root cell suspension treated with 3 mM tyrosol produced maximum salidroside content (26.62 mg/g DW) on day 12. Moreover, the total phenolics content increased significantly (44.21 mg/g DW) on day 12 in 3 mM tyrosol treatment under photoperiod (16L/8D h). However, precursor concentrations did not influence the total flavonoids content. The present investigation suggests that the immediate pathway precursor, tyrosol, has a strong effect on enhanced production of salidroside, irrespective of explant type and light regimes.

Optimization of Biomass Accumulation and Production of Phenolic Compounds in Callus Cultures of Rhodiola rosea L. Using Design of Experiments

Rhodiola rosea L. is a valuable medicinal plant with adaptogenic, neuroprotective, antitumor, cardioprotective, and antidepressant effects. In this study, design of experiments methodology was employed to analyze and optimize the interacting effects of mineral compounds (concentration of NO₃⁻ and the ratio of NH₄⁺ to K⁺) and two plant growth regulators [total 6-benzylaminopurine (BAP) and α-naphthylacetic acid (NAA) concentration and the ratio of BAP to NAA] on the growth and the production of total phenolic compounds (TPCs) in R. rosea calluses. The overall effect of the model was highly significant (p < 0.0001), indicating that NH₄⁺, K⁺, NO₃⁻, BAP, and NAA significantly affected growth. The best callus growth (703%) and the highest production of TPCs (75.17 mg/g) were achieved at an NH₄⁺/K⁺ ratio of 0.33 and BAP/NAA of 0.33, provided that the concentration of plant growth regulators was 30 μM and that of NO₃⁻ was ≤40 mM. According to high-performance liquid chromatography analyses of aerial parts (leaves and stems), in vitro seedlings and callus cultures of R. rosea contain no detectable rosarin, rosavin, rosin, and cinnamyl alcohol. This is the first report on the creation of an experiment for the significant improvement of biomass accumulation and TPC production in callus cultures of R. rosea.

New biological trends on cell and callus growth and azadirachtin production in Azadirachta indica

Azadirachtin is an important secondary metabolite from Azadirachta indica used as a natural biopesticide. This study is the first comprehensive report concerning the influence of plant growth regulators on callus induction, cell suspension growth, and azadirachtin accumulation and production in cell suspension cultures of A. indica. We investigated the effect of plant growth regulators including different types of auxins and cytokinins and their combinations on callus induction, cell suspension growth, and azadirachtin accumulation and production. The highest percentage of callusing (100%) obtained at different combinations of plant growth regulators on MS medium supplemented with 1 mg/L picloram and 2 mg/L kinetin and the highest fresh weight of callus (264.50 mg) was observed in MS medium containing 1.5 mg/L NAA and 3 mg/L kinetin. In cell suspension cultures, the maximum cell density, SCV, and PCV were 2.44 × 10⁶ cells per mL, 97.95%, and 81.46%, respectively, obtained in the MS medium containing 1.5 mg/L 2,4-D and 3 mg/L zeatin riboside. The highest average growth rate (0.25 days) was on MS medium containing 1.5 mg/L NAA and 3 mg/L zeatin riboside. The MS medium supplemented with 1 mg/L picloram and 2 mg/L kinetin produced the highest amount of fresh cell weight (493.02 g/L), dry cell weight (77.27 g/L), azadirachtin accumulation (3.69 mg/gDW), and azadirachtin production (285.64 mg/L). The results showed that all measured indices had positive correlation with together except FCW and DCW with azadirachtin accumulation.