Transgene-free gene editing in Capsicum annuum using carbon nanotube-mediated Cas9 delivery

Overview

This research presents a novel approach to gene editing in Capsicum annuum (pepper) that eliminates the need for integrating foreign DNA into the plant genome. By leveraging carbon nanotube (CNT) technology to deliver Cas9 and guide RNAs directly into meristematic tissues, the method enables transgene-free, heritable gene editing. This breakthrough addresses a major bottleneck in pepper and other transformation-recalcitrant crops, where conventional genetic engineering approaches are inefficient or impractical. The technology has significant implications for precision breeding, trait development, and the production of gene-edited crops that are not classified as genetically modified organisms in many regulatory frameworks.

Technical specifications

Key features:

• Carbon nanotube-mediated delivery of plasmid DNA into plant cells, enabling transient expression without genomic integration
• Meristem-specific Cas9 expression targeting shoot apical meristems (SAM), axillary buds, and pollen
• Validated GFP expression in both spinach and pepper root tips via CNT transfection of imbibed embryos
• qPCR-confirmed Cas9 expression in pepper SAMs, with peak expression detected 24 hours post-transfection
• Plasmid constructs designed to target the phytoene desaturase (PDS) gene, which produces a visible photobleaching phenotype when knocked out
• Experimental design includes appropriate controls (CNT-only, plasmid-only, and GFP) with triplicate replicates across multiple timepoints

Applications:

• Gene editing in transformation-recalcitrant species and genotypes
• Precision breeding of pepper and potentially other Solanaceae crops
• Development of transgene-free edited varieties for regulatory and market acceptance
• Trait improvement through targeted gene knockouts

Technology readiness level

This technology is currently at an early-to-mid stage of development (TRL 3-4). Proof-of-concept has been demonstrated through successful GFP expression in pepper and spinach, and Cas9 expression has been confirmed in pepper shoot apical meristems via qPCR. Preliminary data also suggests expression in axillary buds and pollen. The next phase of validation will focus on demonstrating actual gene editing by targeting the PDS gene to produce a visible photobleaching phenotype. Additional work will assess editing efficiency across different meristem types and verify heritability through genotyping and selfing of T1 generations. A budget of $15,000 is required to complete these validation experiments.