Generation of CRISPR-edited birch plants without DNA integration using Agrobacterium-mediated transformation technology

CRISPR/Cas9 system has emerged as a powerful tool in genome editing; however, generation of CRISPR-edited DNA-free plants is still challenging. In this study, Betula platyphylla (birch) was used to build a method to generate CRISPR-edited plant without foreign DNA integration using Agrobacterium-mediated transformation (CPDAT method). This technique utilizes transient genetic transformation to introduce T-DNA coding gRNA and Cas9 into birch cells, and T-DNA will express to synthesize gRNA and Cas9 protein, which will form a complex to cleave the target DNA site. The genome may be mutated due to DNA repair, and these mutations will be preserved and accumulated not dependent on whether T-DNA is integrated into the genome or not. After transient transformation, birch plants were cut into explants to induce adventitious buds without antibiotic selection pressure. Each adventitious bud can be considered as an independent potentially CRISPR-edited line for mutation detection. CRISPR-edited birch plants without foreign DNA integration are further selected by screening CRISPR-edited lines without T-DNA integration. Among 65 randomly chosen independent lines, the mutation rate was 80.00% including 40.00% of lines with both alleles mutated. In addition, 5 lines out of 65 studied lines (7.69%) were CRISPR-edited birch plants without DNA integration. In conclusion, this innovative method presents a novel strategy for generating CRISPR-edited birch plants, thereby significantly enhancing the efficiency of generating common CRISPR-edited plants. These findings offer considerable potential to develop plant genome editing techniques further.