Highly efficient Agrobacterium rhizogenes-mediated gene editing system in Salvia miltiorrhiza inbred line bh2-7

The CRISPR/Cas9 system is a powerful tool for genomic editing with significant potential for gene function validation and molecular breeding in medicinal plants. Salvia miltiorrhiza, a model medicinal plant, was among the pioneers to utilize CRISPR/Cas9 technology, though achieving high-efficiency homozygous knockout mutants has been challenging. In this study, the analysis of variations at 241 single-guide RNA (sgRNA) across different reference genomes and experimental materials was conducted first, leading to the identification of the six-generation inbred line bh2-7 as the most suitable reference genome and experimental material for gene editing research in S. miltiorrhiza. Next, five Agrobacterium rhizogenes strains were evaluated for hairy root induction, editing efficiency, and mutation patterns, with C58C1 and K599 emerging as the most effective delivery systems. Using the CRISPR/Cas9 vector pZKD672, 53 target sites were successfully edited, with K599 achieving 71.07% editing efficiency and 36.74% homozygous or biallelic (HOM) efficiency and C58C1 showing 62.27% editing efficiency and 23.61% HOM efficiency. We thus constructed a large-scale mutant library targeting 121 genes with 170 sgRNAs, yielding 1664 homozygous or biallelic mutants. Analysis of 65 low-efficiency target sites revealed that sgRNA mismatches and secondary structures were key factors reducing HOM efficiency, offering insights for future target design. This study establishes an efficient CRISPR/Cas9 system, advancing precision breeding and metabolic engineering research in medicinal plants.