Development of an Agrobacterium-delivered codon-optimized CRISPR/Cas9 system for chickpea genome editing
Chickpea is considered recalcitrant to in vitro tissue culture. The Clustered, Regularly Interspaced Short Palindromic Repeats/CRISPR-associated protein 9 (CRISPR/Cas9) based genome editing in chickpea can remove the bottleneck of limited genetic variation in this cash crop rich in nutrients and protein. However, the generation of stable mutant lines using CRISPR/Cas9 requires efficient and highly reproducible transformation approaches. We modified a binary vector pPZP200 by introducing a codon-optimized Cas9 gene for chickpea and the promoters of Medicago truncatula U6 snRNA for expressing guide RNA targeted to the Phytoene Desaturase (PDS) gene. The dissected single cotyledons with half embryo of chickpea were used as explants for genetic transformation. A single gRNA was found sufficient to achieve high efficiency (42%) editing with the generation of PDS mutants with albino phenotypes. A simple, rapid, highly reproducible, stable transformation and CRISPR/Cas9-based genome editing system for chickpea was established. For the first time, this study aimed to demonstrate this systems applicability by performing a gene knockout of the chickpea phytoene desaturase gene (CaPDS) in stable shoots using an improved chickpea transformation protocol.