Glycoalkaloid-Free Starch Potatoes Generated by CRISPR/Cas9-Mediated Mutations of Genes in the Glycoalkaloid Biosynthesis Pathway Enable More Sustainable Uses of By-Products From Starch Production.

Steroidal glycoalkaloids (SGAs) are toxic cholesterol-derived secondary metabolites present in several Solanaceae species. In potato, tuber SGA levels are for reasons of toxicity of concern in both table and starch cultivars. In the latter, SGAs bind to proteins and fibres in starch production side-streams and prevent their further uses as food and feed. To enable more sustainable uses of starch by-products, we have here reduced SGA biosynthesis in a starch potato cultivar using DNA-free CRISPR/Cas9. Six SGA genes were targeted, encoding enzymes acting either before cholesterol (SMO1-L, DWF1-L, DWF7-L), or after (16DOX, CYP88B1, TAMiso2). Editing efficiencies varied between 20% and 49%, and generated mutants were investigated under greenhouse and field conditions. Target mass-spectrometric analyses confirmed reduced SGA levels and alterations of sterol metabolism in mutated events. Plant height and tuber yield were reduced in several events, although this was not correlated to low SGA levels. Several knockout mutants had almost SGA-free leaves and tubers, the latter also under two SGA-inducing conditions. Similarly, both fibre and protein fractions isolated from side-streams in the starch production process from mutant tubers had very low SGA levels. By contrast, the corresponding wild-type SGA levels were almost 10-fold and, respectively, 40-fold higher than the recommended upper safe limit. The results demonstrate that glycoalkaloid-free mutants can be generated and grown with moderate yield reductions under both greenhouse and field conditions. This suggests a potential for sustainable production of high-value products, e.g., food-grade protein and fibre, from starch production side-streams of SGA knockout tubers.