Next Generation Sequencing Bulk Segregant Analysis of Potato Support that Differential Flux into the Cholesterol and Stigmasterol Metabolite Pools Is Important for Steroidal Glycoalkaloid Content

Potatoes and other Solanaceae species produce biologically active secondary metabolites called steroidal glycoalkaloids (GAs) which have antimicrobial, fungicidal, antiviral and insecticidal properties. GAs are, however, also toxic to animals and humans. Compared to wild species of potato, the elite cultivars primarily used for everyday consumption have very low contents of GAs. Breeding for important agronomical traits, like e.g. pathogen resistance, often requires the use of wild species and a situation where offspring have unacceptable high contents of GAs quite frequently arises. Knowledge of metabolic pathways leading to the synthesis of GAs, as well as of the genes that are responsible for the observed differences in plant and tuber GA content is only partial. The primary purpose of this study was to identify genomic regions and candidate genes responsible for differential GA content within a diploid potato mapping population (n = 90) that shows a high variation in GA accumulation. The analysis was performed using a novel method based on next generation genome sequencing. A region on chromosome 1 was found to be associated with differential GA content. Within that region, sterol 24-C-methyltransferase (SMT1), sterol desaturase (SD) and C-4 sterol methyl oxidase (SMO) genes were found, all encoding critical enzymes in the synthesis of the GAs precursor cholesterol. Potatoes and other Solanaceae species produce biologically active secondary metabolites called steroidal glycoalkaloids (GAs) which have antimicrobial, fungicidal, antiviral and insecticidal properties. GAs are, however, also toxic to animals and humans. Compared to wild species of potato, the elite cultivars primarily used for everyday consumption have very low contents of GAs. Breeding for important agronomical traits, like e.g. pathogen resistance, often requires the use of wild species and a situation where offspring have unacceptable high contents of GAs quite frequently arises. Knowledge of metabolic pathways leading to the synthesis of GAs, as well as of the genes that are responsible for the observed differences in plant and tuber GA content is only partial. The primary purpose of this study was to identify genomic regions and candidate genes responsible for differential GA content within a diploid potato mapping population (n = 90) that shows a high variation in GA accumulation. The analysis was performed using a novel method based on next generation genome sequencing. A region on chromosome 1 was found to be associated with differential GA content. Within that region, sterol 24-C-methyltransferase (SMT1), sterol desaturase (SD) and C-4 sterol methyl oxidase (SMO) genes were found, all encoding critical enzymes in the synthesis of the GAs precursor cholesterol.