Abstract
Withania somnifera is one of the most valuable medicinal plants synthesizing secondary metabolites known as withanolides. Despite pharmaceutical importance, limited information is available about the biosynthesis of withanolides. Chemo-profiling of leaf and root tissues of Withania suggest differences in the content and/or nature of withanolides in different chemotypes. To identify genes involved in chemotype and/or tissue-specific withanolide biosynthesis, we established transcriptomes of leaf and root tissues of distinct chemotypes. Genes encoding enzymes for intermediate steps of terpenoid backbone biosynthesis with their alternatively spliced forms and paralogous have been identified. Analysis suggests differential expression of large number genes among leaf and root tissues of different chemotypes. Study also identified differentially expressing transcripts encoding cytochrome P450s, glycosyltransferases, methyltransferases and transcription factors which might be involved in chemodiversity in Withania. Virus induced gene silencing of the sterol ∆7-reductase (WsDWF5) involved in the synthesis of 24-methylene cholesterol, withanolide backbone, suggests role of this enzyme in biosynthesis of withanolides. Information generated, in this study, provides a rich resource for functional analysis of withanolide-specific genes to elucidate chemotype- as well as tissue-specific withanolide biosynthesis. This genomic resource will also help in development of new tools for functional genomics and breeding in Withania.
Highlights
Due to immense importance of W. somnifera in ancient and modern medicinal systems, this plant has been selected under sequencing of 100 genomes of Solanaceae plants in Sol Genomics Network
The transcriptome data, generated in this study, is highly valuable to shed light on the withanolide biosynthesis pathway, gene families involved in specific withanolide biosynthesis, chemodiversity, paralogs of genes involved in terpenoid biosynthesis pathway as well as molecular marker studies
Functional Gene Ontology (GO) assignments represented a large number of the diverse GO terms to unigenes which highlights the diversity of genes represented in Withania transcriptome data (Fig. 3)
Summary
Due to immense importance of W. somnifera in ancient and modern medicinal systems, this plant has been selected under sequencing of 100 genomes of Solanaceae plants in Sol Genomics Network (http://solgenomics.net/ organism/sol100/view). In past, using Next-Generation Sequencing (NGS) a number of transcriptome datasets have been developed and used for discovery and prediction of genes involved in the secondary metabolite biosynthesis from various medicinally important plants[17,18,19,20,21,22]. Transcriptome sequence of leaf and root tissue of one of Withania chemotype (NMITLI-101) was established[23]. This limited information (only one chemotype) restricts the understanding of the chemotype-specific withanolide biosynthesis as well as its correlation with chemo-diversity in Withania. To unravel the biosynthesis of specific withanolides transcriptome datasets of leaf and root tissues of distinct chemotypes have been established. The genomic resource, genes linked to chemodiversity and tools for functional genomics, developed in this study, will help in establishing withanolides biosynthetic pathway and pave a way towards enhanced biosynthesis of the specific withanolides through synthetic biology approach
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