WRKY1-mediated regulation of tryptophan decarboxylase in tryptamine generation for withanamide production in Withania so
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ORIGINAL ARTICLE
WRKY1‑mediated regulation of tryptophan decarboxylase in tryptamine generation for withanamide production in Withania somnifera (Ashwagandha) Jyoti Singh Jadaun1 · Amit Kumar Kushwaha1 · Neelam S. Sangwan1,2 · Lokesh Kumar Narnoliya1 · Smrati Mishra1 · Rajender Singh Sangwan1,3 Received: 21 April 2020 / Revised: 14 July 2020 / Accepted: 22 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Key message WsWRKY1-mediated transcriptional modulation of Withania somnifera tryptophan decarboxylase gene (WsTDC) helps to regulate fruit-specific tryptamine generation for production of withanamides. Abstract Withania somnifera is a highly valued medicinal plant. Recent demonstration of novel indolyl metabolites called withanamides in its fruits (berries) prompted us to investigate its tryptophan decarboxylase (TDC), as tryptophan is invariably a precursor for indole moiety. TDC catalyzes conversion of tryptophan into tryptamine, and the catalytic reaction constitutes a committed metabolic step for synthesis of an array of indolyl metabolites. The TDC gene (WsTDC) was cloned from berries of the plant and expressed in E. coli. The recombinant enzyme was purified and characterized for its catalytic attributes. Catalytic and structural aspects of the enzyme indicated its regulatory/rate-limiting significance in generation of the indolyl metabolites. Novel tissue-wise and developmentally differential abundance of WsTDC transcripts reflected its preeminent role in withanamide biogenesis in the fruits. Transgenic lines overexpressing WsTDC gene showed accumulation of tryptamine at significantly higher levels, while lines silenced for WsTDC exhibited considerably depleted levels of tryptamine. Cloning and sequence analysis of promoter of WsTDC revealed the presence of W-box in it. Follow-up studies on isolation of WsWRKY1 transcription factor and its overexpression in W. somnifera revealed that WsTDC expression was substantially induced by WsWRKY1 resulting in overproduction of tryptamine. The study invokes a key role of TDC in regulating the indolyl secondary metabolites through enabling elevated flux/supply of tryptamine at multiple levels from gene expression to catalytic attributes overall coordinated by WsWRKY1. This is the first biochemical, molecular, structural, physiological and regulatory description of a fruit-functional TDC. Keywords Tryptophan · Tryptamine · Tryptophan decarboxylase · Transcription factor · Serotonin · Withanamides · Withania somnifera
Introduction Communicated by Neal Stewart. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00299-020-02574-4) contains supplementary material, which is available to authorized users.
Withania somnifera Dunal (Solanaceae), one of the most important Indian medicinal plants, produces novel group of steroidal phytochemicals called withanolides, the C28
* Neelam S. Sangwan [email protected]
2
Department of Biochemistry, Central University of Haryana, Mahenderg
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