Streamlined protoplast transfection system for in-vivo validation and transgene-free genome editing in Banana

The advancement in the CRISPR/Cas system has significantly streamlined genome editing in plants, rendering it simple, reliable, and efficient. However, the development of transgene-free crops is a challenging task for vegetatively propagated plants like banana. In the present study, we established banana protoplasts-based versatile and efficient platform for genome editing to overcome this limitation. Herein, a protocol has been optimized for protoplast isolation by considering leaf and embryogenic cell suspension (ECS) of banana cultivar Grand Naine. Freshly prepared ECS was identified as the best source for protoplast isolation. The protoplast viability and competency were checked by transfection with plasmid and RNP complex. Polyethylene glycol (PEG)-mediated protoplast transfection using pCAMBIA1302 and pJL50TRBO vectors showed GFP expression with 30 and 70% efficiency, respectively, eventually proving the protocol's efficacy. Further, gRNAs targeting banana β-carotene hydroxylase gene are validated by in-vitro cleavage test and subsequently used for RNP complex formation with varied ratios (1:1, 1:2, 1:5, and 1:10) of SpCas9 to gRNA1. Among these, a 1:2 molar ratio proved best to generate indel frequency with 7%. Sequencing analysis of the target amplicon revealed mutations upstream of the PAM region, specifically with gRNA1, among the three in-vitro validated gRNAs. This study evaluated the effectiveness of gRNAs in-vitro and in-vivo, yielding inconsistent results that highlight the need for comprehensive in-vivo validation of their functionality. Conclusively, the optimized protocol for banana transfection has the potential to be harnessed for the generation of transgene-free genetically improved banana.