Highly Efficient Homozygous CRISPR/Cas9 Gene Editing Based on Single-Cell-Originated Somatic Embryogenesis in Liriodendron tulipifera

The clustered, regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein (Cas) system is the most widely used gene-editing tool to date. However, its application in the genetic improvement of forestry trees has been largely limited. Here, we first established a highly efficient multi-target editing system in the magnoliid woody plant <i>Liriodendron tulipifera</i>. Using <i>phytoene desaturase</i> gene (<i>PDS</i>) as an example, we systematically compared CRISPR/Cas9 and CRSPR/Cpf1 expression systems for loss-of-function analysis and conducted genetic transformations using transient and stable transformation. Ultimately, our findings indicated that the CRISPR/Cas9 system, when applied to transformation based on single-cell-originated somatic embryogenesis, yielded the highest gene-editing efficiency, with mutation rates of nearly 100%. Furthermore, we obtained a total of 137 regeneration plantlets via somatic embryogenesis, of which 82.48% exhibited an albino phenotype. The Illumina sequencing results of albino seedlings and the callus tissue obtained from dedifferentiation of mutant plants revealed that the mutation at the T1 target site was homozygous. These results indicate that CRISPR/Cas9-based multiplex genome-editing technology can not only accelerate the identification of gene function but also be incorporated into the genetic improvement and breeding of tulip trees, supporting the scale propagation of genome-edited plantlets via somatic embryogenesis.