The cultivated potato, Solanum tuberosum L., has been one of the world’s most important food crops for more than 190 years and may become even more important to global food security in the coming 20 - 30 years. One of the world's largest growing health concerns is not just the availability of food in the coming years but also food’s nutritional quality. Micronutrient malnutrition is a serious global health concern linked to life threatening illness and may affect as many as two billion people. Staple crops that are poor sources of vitamins and minerals must be improved to provide a reasonable quality of life for populations that suffer micronutrient deficiencies. Folate (a.k.a. vitamin B9) is essential in the human diet and without adequate folate intake several serious health concerns such as congenital birth defects and an increased risk of stroke and heart disease can occur. Folate intake of the majority of the population remains sub-optimal even in countries that have implemented folic acid food fortification. Potato represents an appropriate crop for biofortification because of its high consumption worldwide and also because modern potatoes contain low amounts of folate.
The purpose of this research is to further explore folates' natural diversity within potato germplasm, better understand the regulation of folate levels, and to begin the development of molecular tools to assist breeding efforts that aim at increased folate content in the commercial potato cultivars. These efforts will help to alleviate folate deficiency in the United States and abroad.
Two hundred and fifty individual plants from 77 accessions and 10 Solanum species were screened for their folate content using a tri-enzyme extraction and microbial assay. The screening focused on species that had been previously shown to have individuals with high folate content. These species were Solanum tuberosum subsp. andigenum, Solanum vernei and Solanum boliviense. Other species that had never been analyzed for folate content before, S. stipuloideum, S. chacoense subsp. chacoense, S. candolleanum, S. acaule, S. demissum, S. microdontum, and S. okadae, were also evaluated. There was a 10-fold range of folate concentrations among individuals tested. Certain individuals within the species Solanum tuberosum subsp. andigenum, Solanum vernei and Solanum boliviense have the potential to produce more than double the folate concentrations of commercial cultivars such as Russet Burbank. These results show that exploring the genetic diversity of potato identified potential high folate sources for further introgression into modern day cultivars.
In order to better understand the regulatory mechanisms that control folate accumulation in potato tubers, the expression of genes involved in folate metabolism was determined in high and low folate tuber samples using RNA-sequencing (RNA-Seq) and real time quantitative RT-PCR (qPCR) analyses. RNA-Seq analysis showed that, among folate biosynthesis and salvage genes, γ-glutamyl hydrolase 1 (GGH1) was consistently expressed at higher levels in high folate compared to low folate segregants of a Solanum boliviense accession. qPCR analysis was used to determine GGH1 expression in eight additional pairs of folate segregants. Results showed that GGH1 transcripts levels were higher in high folate compared to low folate segregants for seven out of eight pairs of folate segregants analyzed. These results suggest that GGH1 gene expression may be a determinant of folate content in potato tubers and may be considered as a target for folate engineering.
An F2 population of 94 individuals from a cross between a high and a low folate genotype was evaluated for folate content and genotyped for single nucleotide polymorphism (SNP) markers. More than 3,000 high quality SNPs were used to construct linkage maps. SNP-trait association analysis and QTL single marker analysis was performed to identify SNPs and genomic regions associated with high folate content. SNPs associated with folate content were located on chromosomes 3, 6, and 7. Future research should focus on validating these SNP markers.