In Vitro Propagation of Withania somnifera (L.) Dunal

Differential Gene Expression and Withanolides Biosynthesis During in vitro and ex vitro Growth of Withania somnifera (L.) Dunal

Ashwagandha (Withania somnifera L. Dunal) is a medicinally important plant with withanolides as its major bioactive compounds, abundant in the roots and leaves. We examined the influence of plant growth regulators (PGRs) on direct organogenesis, adventitious root development, withanolide biosynthetic pathway gene expression, withanolide contents, and metabolites during vegetative and reproductive growth phases under in vitro and ex vitro conditions. The highest shooting responses were observed with 6-benzylaminopurine (BAP) (2.0 mg L^-1) + Kinetin (KIN) (1.5 mg L^-1) supplementation. Furthermore, BAP (2.0 mg L^-1) + KIN (1.5 mg L^-1) + gibberellic acid (GA₃) (0.5 mg L^-1) exhibited better elongation responses with in vitro flowering. Half-strength MS medium with indole-3-butyric acid (IBA) (1.5 mg L^-1) exhibited the highest rooting responses and IBA (1.0 mg L^-1) with highest fruits, and overall biomass. Higher contents of withaferin A (WFA) [∼8.2 mg g^-1 dry weight (DW)] were detected in the reproductive phase, whereas substantially lower WFA contents (∼1.10 mg g^-1 DW) were detected in the vegetative phase. Cycloartenol synthase (CAS) (P = 0.0025), sterol methyltransferase (SMT) (P = 0.0059), and 1-deoxy-D-xylulose-5-phosphate reductase (DXR) (P = 0.0375) genes resulted in a significant fold change in expression during the reproductive phase. The liquid chromatography-mass spectrometry (LC-MS) analysis revealed metabolites that were common (177) and distinct in reproductive (218) and vegetative (167) phases. Adventitious roots cultured using varying concentrations of indole-3-acetic acid (IAA) (0.5 mg L^-1) + IBA (1.0 mg L^-1) + GA₃ (0.2 mg L^-1) exhibited the highest biomass, and IAA (0.5 mg L^-1) + IBA (1.0 mg L^-1) exhibited the highest withanolides content. Overall, our findings demonstrate the peculiarity of withanolide biosynthesis during distinct growth phases, which is relevant for the large-scale production of withanolides.

Addressing Challenges to Enhance the Bioactives of Withania somnifera through Organ, Tissue, and Cell Culture Based Approaches

Withania somnifera is a highly valued medicinal plant in traditional home medicine and is known for a wide range of bioactivities. Its commercial cultivation is adversely affected by poor seed viability and germination. Infestation by various pests and pathogens, survival under unfavourable environmental conditions, narrow genetic base, and meager information regarding biosynthesis of secondary metabolites are some of the other existing challenges in the crop. Biotechnological interventions through organ, tissue, and cell culture provide promising options for addressing some of these issues. In vitro propagation facilitates conservation and sustainable utilization of the existing germplasms and broadening the genetic base. It would also provide means for efficient and rapid mass propagation of elite chemotypes and generating uniform plant material round the year for experimentation and industrial applications. The potential of in vitro cell/organ cultures for the production of therapeutically valuable compounds and their large-scale production in bioreactors has received significant attention in recent years. In vitro culture system further provides distinct advantage for studying various cellular and molecular processes leading to secondary metabolite accumulation and their regulation. Engineering plants through genetic transformation and development of hairy root culture system are powerful strategies for modulation of secondary metabolites. The present review highlights the developments and sketches current scenario in this field.