CRISPR–Cas9 System for Genome Engineering of Photosynthetic Microalgae

Targeted genome editing using RNA-guided endonucleases is an emerging tool in algal biotechnology. Recently, CRISPR–Cas systems have been widely used to manipulate the genome of some freshwater and marine microalgae. Among two different classes, and six distinct types of CRISPR systems, Cas9-driven type II system has been widely used in most of the studies for targeted knock-in, knock-out and knock-down of desired genes in algae. CRISPR technology has been demonstrated in microalgae including diatoms to manifest the function of the particular gene (s) and developing industrial traits, such as improving lipid content and biomass productivity. Instead of these, there are a lot of gears to be defined about improving efficiency and specificity of targeted genome engineering of microalgae using CRISPR–Cas system. Optimization of tools and methods of CRISPR technology can undoubtedly transform the research toward the industrial-scale production of commodity chemicals, food and biofuels using photosynthetic cell factories. This review has been focused on the efforts made so far to targeted genome engineering of microalgae, identified scopes about the hurdles related to construction and delivery of CRISPR–Cas components, algae transformation toolbox, and outlined the future prospect toward developing the CRISPR platform for high-throughput genome-editing of microalgae.