*Review* **Modern Trends in Plant Genome Editing: An Inclusive Review of the CRISPR**/**Cas9 Toolbox**

**Ali Razzaq <sup>1</sup> , Fozia Saleem <sup>1</sup> , Mehak Kanwal <sup>2</sup> , Ghulam Mustafa <sup>1</sup> , Sumaira Yousaf <sup>2</sup> , Hafiz Muhammad Imran Arshad <sup>2</sup> , Muhammad Khalid Hameed <sup>3</sup> , Muhammad Sarwar Khan <sup>1</sup> and Faiz Ahmad Joyia 1,\***


Received: 14 June 2019; Accepted: 15 August 2019; Published: 19 August 2019

**Abstract:** Increasing agricultural productivity via modern breeding strategies is of prime interest to attain global food security. An array of biotic and abiotic stressors affect productivity as well as the quality of crop plants, and it is a primary need to develop crops with improved adaptability, high productivity, and resilience against these biotic/abiotic stressors. Conventional approaches to genetic engineering involve tedious procedures. State-of-the-art OMICS approaches reinforced with next-generation sequencing and the latest developments in genome editing tools have paved the way for targeted mutagenesis, opening new horizons for precise genome engineering. Various genome editing tools such as transcription activator-like effector nucleases (TALENs), zinc-finger nucleases (ZFNs), and meganucleases (MNs) have enabled plant scientists to manipulate desired genes in crop plants. However, these approaches are expensive and laborious involving complex procedures for successful editing. Conversely, CRISPR/Cas9 is an entrancing, easy-to-design, cost-effective, and versatile tool for precise and efficient plant genome editing. In recent years, the CRISPR/Cas9 system has emerged as a powerful tool for targeted mutagenesis, including single base substitution, multiplex gene editing, gene knockouts, and regulation of gene transcription in plants. Thus, CRISPR/Cas9-based genome editing has demonstrated great potential for crop improvement but regulation of genome-edited crops is still in its infancy. Here, we extensively reviewed the availability of CRISPR/Cas9 genome editing tools for plant biotechnologists to target desired genes and its vast applications in crop breeding research.

**Keywords:** CRISPR/Cas9; genome editing; plant breeding; multiplex genome editing; crop improvement; TALEN; ZFN; biotic stress; abiotic stress
