Balancing Tuber Vitamin C Improvement with Trade-off Side-effect by Fine-tuning Regulation of StGGPs

Potato (Solanum tuberosum L.) is an important staple crop, worldwide. Due to its highly heterozygous genomes and tetrasomic inheritance, it is very challenging and time-consuming to introduce and fix new traits into cultivars, using traditional breeding strategies. Here, we applied a gene-editing approach to enhance vitamin C (Vc) content in the tuber by mutating the upstream open reading frame (uORF) of two potato GDP-L-galactose phosphorylase (GGP) genes. New variants, with well-balanced nutrient content and yield, were created, and a high level of Vc was retained in these biofortified tubers even after culinary processing. In addition, tubers of these gene-edited lines have a much higher antioxidant activity, and the leaves exhibit enhanced salt tolerance, when compared to the controls. However, we also observed that excessive Vc fortification may perturb auxin biosynthesis, as well as its signal transduction in gene-edited plants, which in turn leads to plant developmental arrest and yield penalties. To perform RNA-seq analysis, total RNA was extracted from S15-65, uorf-StGGP1-A and uorf-StGGP1-B leaves at the seedling stage and tubers in the mature growth period. To elucidate the underlying mechanisms responsible for the imbalanced phenotype of uorf-StGGP1-B, we conducted a comprehensive transcriptome analysis of mature tubers and seedling-stage leaves.