The GE-GGP2 lettuce events were generated by editing the upstream open reading frame (uORF) of GDP-L-galactose phosphorylase (GGP2), a key enzyme in vitamin C biosynthesis.

A CRISPR/Cas9 construct, with a single-guide RNA that targeted the region harboring a uORF initiation codon, was delivered into cotyledon explants of lettuce with Agrobacterium tumefaciens.

Three regenerated mutant lines were analysed; two showed small deletions (up to 14 bp) present proximal to the initiation codon (ACG), but a large deletion (92 bp) in the third line led to the loss of both the initiation codon and a portion of the uORF coding region.

All three mutant lines showed not only increased oxidation stress tolerance, but also significantly increased foliar ascorbate content.