Viral-Based Gene Editing System for Nutritional Improvement of Fructan Content in Lettuce

Lettuce is a globally cultivated and consumed leafy crop. Here we developed an efficient tobacco rattle virus (TRV)-based guide RNA (gRNA) delivery system for CRISPR/Cas editing in the commercial lettuce cultivar 'Noga'. Plants stably expressing Cas9 were inoculated with TRV vectors carrying gRNAs targeting five nutrient-associated genes. The system achieved an average editing efficiency of 48.7%, with up to 78.9% of regenerated plantlets showing independent mutations. This approach eliminates the need for antibiotic selection, simplifying tissue culture processes. The system supports diverse applications, including Cas12a editing and large-fragment deletions using dual gRNA sets. Targeting the fructan 1-exohydrolase 2 (1-FEH2) gene produced knockout lines with significant increases in prebiotic dietary fibre fructan content, up to 5.2-fold, and an average rise in the degree of polymerisation by 2.15 units compared with controls. Combining 1-FEH1 and 1-FEH2 knockouts did not further increase fructan levels, revealing 1-FEH2 as the predominant isozyme in lettuce. RT-qPCR analysis showed reduced expression of the upstream biosynthetic enzyme sucrose:sucrose 1-fructosyl transferase (1-SST), suggesting potential feedback inhibition in fructan metabolism. This TRV-based gene editing approach, utilised here to increase fructan content, could be applied to improve other valuable traits in lettuce, and may inspire similar systems to enhance nutritional content of crops.