Abstract
Tissue specific biosynthesis of secondary metabolites is a distinguished feature of medicinal plants. Withania somnifera, source of pharmaceutically important withanolides biosynthesizes withaferin-A in leaves and withanolide-A in roots. To increase the in planta withanolides production, a sustainable approach needs to be explored. Here, we isolated endophytes from different parts of W. somnifera plants and their promising role in in planta withanolide biosynthesis was established in both in-vivo grown as well in in-vitro raised composite W. somnifera plants. Overall, the fungal endophytes improved photosynthesis, plant growth and biomass, and the root-associated bacterial endophytes enhanced the withanolide content in both in-vivo and in-vitro grown plants by modulating the expression of withanolide biosynthesis genes in leaves and roots. Surprisingly, a few indole-3-acetic acid (IAA)-producing and nitrogen-fixing root-associated endophytes could induce the biosynthesis of withaferin-A in roots by inducing in planta IAA-production and upregulating the expression of withanolide biosynthesis genes especially MEP-pathway genes (DXS and DXR) in roots as well. Results indicate the role of endophytes in modulating the synthesis and site of withanolides production and the selected endophytes can be used for enhancing the in planta withanolide production and enriching roots with pharmaceutically important withaferin-A which is generally absent in roots.
Highlights
Withania somnifera well-known as Indian ginseng or Ashwagandha, is an important medicinal plant widely distributed around the globe and used in traditional medicine systems like Ayurveda, Siddha, Unani and Chinese
It has been observed that treatment with the extract of sea weeds on Withania hairy roots increased the production of withanolides by increasing the expression of key genes of withanolide biosynthesis such as squalene epoxidase (SQE), squalene synthase (SQS), 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR) and farnesyl pyrophosphate synthase (FPPS)[30]
We performed 16S rRNA and internal transcribed spacer (ITS) sequencing for identification of bacterial and fungal endophytes, respectively
Summary
Withania somnifera well-known as Indian ginseng or Ashwagandha, is an important medicinal plant widely distributed around the globe and used in traditional medicine systems like Ayurveda, Siddha, Unani and Chinese. Overexpression of squalene synthase (SQS), a key regulatory gene of withanolide biosynthesis in W. somnifera could increase the content of withaferin A and withanolide A in the leaves up to 4–4.5 fold[23]. It has been observed that treatment with the extract of sea weeds on Withania hairy roots increased the production of withanolides by increasing the expression of key genes of withanolide biosynthesis such as squalene epoxidase (SQE), SQS, 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR) and farnesyl pyrophosphate synthase (FPPS)[30]. Efforts were made to identify the most potent endophytes from W. somnifera plants to decipher their roles in enhancing the plant growth and in parallel, the overall yield of therapeutically important withanolides, through their judicious screening on in-vivo grown plants as well as in in-vitro raised composite plants (i.e., plants with wild-type shoots and wild type Agrobacterium rhizogenes induced transgenic roots, as illustrated previously[44]). Again, several other studies, such as nutrient/hormone uptake, interactions with root nodulating bacteria and mycorrhizal symbiotic association, have documented the competence of this composite plant based technology[46]
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