Optimization of gene editing in cowpea through protoplast transformation and agroinfiltration by targeting the phytoene desaturase gene

Abstract

Cowpea (Vigna unguiculata) is a legume staple widely grown across Sub-Saharan Africa and other tropical and sub-tropical regions. Considering projected climate change and global population increases, cowpea’s adaptation to hot climates, resistance to drought, and nitrogen-fixing capabilities make it an especially attractive crop for facing future challenges. Despite these beneficial traits, efficient varietal improvement is challenging in cowpea due to its recalcitrance to transformation and long regeneration times. Transient gene expression assays can provide solutions to alleviate these issues as they allow researchers to test gene editing constructs before investing in the time and resource- intensive process of transformation. In this study, we developed an improved cowpea protoplast isolation protocol, a transient protoplast assay, and an agroinfiltration assay to be used for initial testing and validation of gene editing constructs and for gene expression studies. To test these protocols, we assessed the efficacy of a CRISPR-Cas9 construct containing four multiplexed single-guide RNA (sgRNA) sequences using polyethylene glycol (PEG)-mediated transformation and agroinfiltration with phytoene desaturase (PDS) as the target gene. Sanger sequencing of DNA from transformed protoplasts and agroinfiltrated cowpea leaves revealed several large deletions in the target sequences. The protoplast system and agroinfiltration protocol developed in this study provide versatile tools to test gene editing components before initiating plant transformation, thus improving the chance of using active sgRNAs and attaining the desired edits and target phenotype.