CRISPR/Cas genome editing to optimize pharmacologically active plant natural products.

Since time immemorial, human use medicinal plants as sources of food, therapy and industrial purpose. Classical biotechnology and recent next-generation sequencing (NGS) techniques have been successfully used to optimize plant-derived natural-products of biomedical significance. Earlier, protein based editing tools viz. zinc-finger nucleases (ZFNs) and transcription activator-like endonucleases (TALENs) have been popularized for transcriptional level genome manipulation. Clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated9 (Cas9) endonuclease system is an efficient, robust and selective site-directed mutagenesis strategy for RNA-guided genome-editing. CRISPR/Cas9 genome-editing tool employs designed guide-RNAs that identifies a 3 base-pair protospacer adjacent motif (PAM) sequence occurring downstream of the target-DNA. The present review comprehensively complies the recent literature (2010-2020) retrieved from scientific-databases on the application of CRISPR/Cas9-editing-tools as potent genome-editing strategies in medicinal-plants discussing the recent developments, challenges and future-perspectives with notes on broader applicability of the technique in plants and lower-organisms. In plants, CRISPR/Cas-editing has been implemented successfully in relation to crop-yield and stress-tolerance. However, very few medicinal plants have been edited using CRISPR/Cas genome tool owing to the lack of whole-genome and mRNA-sequences and shortfall of suitable transformation and regeneration strategies. However, recently a number of plant secondary metabolic-pathways (viz. alkaloid, terpenoid, flavonoids, phenolic, saponin etc.) have been engineered employing CRISPR/Cas-editing via knock-out, knock-in, point-mutation, fine-tuning of gene-expression and targeted-mutagenesis. This genome-editing tool further extends its applicability incorporating the tools of synthetic- and systems-biology, functional-genomics and NGS to produce genetically-engineered medicinal-crops with advanced-traits facilitating the production of pharmaceuticals and nutraceuticals.