Advances in Delivery of CRISPR–Cas Reagents for Precise Genome Editing in Plants

The human population is growing rapidly and is projected to reach 10 billion by 2055 according to The World Bank. However, limited cultivable land, climate change, and plant diseases are impeding crop yield improvement necessary to feed the growing population. This presents a grand challenge for breeders and farmers who must sustain production to accommodate the population numbers in a race against time. Precision and rapid breeding are effective ways to tackle this challenge. While conventional genetic-engineering (GE) technology is an important approach in modern plant breeding, the process of producing GE products is extremely laborious and time-consuming. Additionally, these GE products face a lengthy government regulation process before their release and commercialization. They also have a history of being poorly received by consumers. The new generation of genome-editing platforms, particularly the clustered regularly interspaced short palindromic repeats-associated proteins (CRISPR–Cas)-based technology, has revolutionized bioscience fields. Compared to conventional GE, CRISPR–Cas displays several advantages. It has a simple design that allows it to target specific regions of DNA in living cells with high efficiency and lower costs than other methods. However, many factors could affect the success and efficiency of CRISPR–Cas-mediated plant genome editing. One of the challenges of using CRISPR–Cas to edit plant genomes is delivering the CRISPR components into plant cells, which are protected by cell walls. The goal of this chapter is to examine how CRISPR–Cas biomolecules can be introduced into plants using different methods. We will compare and contrast three main methods: Agrobacterium-mediated delivery, biolistic (or particle-bombardment)-based delivery, and protoplast-based delivery. New approaches, such as using nanoparticles as carriers, will be showcased as well. We will also discuss the advantages and disadvantages of using different formats (DNA, RNA, and RNP) of CRISPR–Cas reagents for each method.