Altered Steroidal Glycoalkaloid (SGA) Biosynthesis in Diploid Potatoes as Induced by EMS-mutagenesis
Crop Breed Genet Genom. 2020;2(4):e200017. https://doi.org/10.20900/cbgg20200017
Plain language summary
Potatoes can contain toxic compounds known as steroidal glycoalkaloids (SGA), if not properly bred-out during cultivar development. Potato products that contain more than 100 mg SGA/100 g dry weight can be toxic to humans. Wild potatoes are prone to contain more SGA than cultivated potatoes but they carry hidden genetic characteristics needed in potato breeding. In this study, the team hypothesized that random mutagenesis can reduce SGA production in wild potato germplasm that can be used as pre-breeding plant materials. They used 1,750 mutant potato clones as starting plant material generated by treating wild true potato seeds using a chemical mutagen. After genetic and chemical analyses, the team identified 9 mutated genes in the SGA biosynthetic routes, determined the frequency and nature of the mutations in 246 lines, of which 14% showed SGA content lower than the wild types and commercial check varieties. The authors finally compared the whole genome gene expression of a mutant low in SGA and a wild type high in SGA and reported a contrasted expression profiles in SGA biosynthetic pathways. The study is a first to generate and characterize a large mutant diploid wild germplasm collection and to show an effective alteration of SGA production, paving the way for more detailed functional analysis for other agronomic traits and for developing mutant diploid potato cultivars.
Steroidal glycoalkaloids (SGAs) can be toxic to humans at more than 100 mg/100 g dry weight of potato tubers. The objective of the current study was to characterize phenotypically and genotypically a subset of 1,750 ethyl methane sulfonate (EMS)-mutagenized diploid potato clones previously reported in our group for altered SGA production. The study reports on a wide range of SGA profiles in 246 EMS-mutant lines, of which 14% showed lower SGA content than the wild types and commercial varieties. An Ampliseq gene panel sequencing of 9 key SGA biosynthetic genes from 87 EMS-treated lines showing varied SGA profiles revealed 61 unique functional SNP mutations in 56 unique EMS-treated individual lines. Mutational frequencies in the target genes ranged from 1/16 kb (SGT2) to 1/341 kb (GAME7), with an average of 1/47 kb. Among these mutations, mutations were detected in GAME7, GAME6, GAME11, GAME4CH6, GAME4CH12, and SGT3 genes of low SGA EMS-treated lines, genes deemed essential for steroidal aglycone hydroxylation, oxidation, and solanidine glycosylation. Subsequent comparative transcriptomic analysis of a low SGA mutant line and a high SGA wild type line showed significant downregulation of UDP-glycosyltransferases and cytochrome P450s expression in the low SGA EMS-mutant line. Using EMS-mutagenesis, this study is the first to show evidence of an effective alteration of SGA production in diploid potato tubers and paves the way for more functional analysis of this mutant population as well as diploid mutant potato cultivar development.