CRISPR/Cas technologies have revolutionized plant genome editing, yet their inherent bias toward small insertions or deletions (indels) limits their utility for dissecting regulatory elements and generating impactful allelic variants. Here, we report the development and systematic evaluation of exonuclease-fused CRISPR/Cas systems in soybean to overcome this limitation. We engineered fusions of Cas9 and Cas12a with bacteriophage T5 exonuclease and human TREX2 and assessed their editing performance at the GmWOX5 locus using Agrobacterium rhizogenes-mediated transformation and deep amplicon sequencing. While native Cas9 and Cas12a predominantly generated micro-size deletions (1–10 bp), T5-Exo fusions shifted the mutation spectrum, producing a high frequency of moderate (26–50 bp) and large (> 50 bp) deletions. TREX2 fusions preferentially enhanced the generation of small (11–25 bp) to moderate deletions (26–50 bp). Fusion of exonucleases to Cas9 substantially reduced insertion frequencies and promoted more precise deletion patterns, as observed in T5-Exo-Cas9 and TREX2-Cas9. Deletions from both exonuclease fusions were biased toward the PAM-proximal region, reflecting altered repair outcomes likely driven by directional exonuclease activity and enhanced end resection. These results demonstrate that exonuclease fusions effectively expand the CRISPR toolkit by enabling efficient, targeted generation of larger deletions, which are often required for targeting cis-regulatory elements and microRNAs. We demonstrate that engineered exonuclease-fused CRISPR systems enable efficient, target-specific large deletions in soybean, providing a valuable tool to enhance functional genomics and accelerate trait discovery in crops.
Devkar et al. (Thu,) studied this question.