Expression levels of the y-glutamyl hydrolase I gene predict vitamin B9 content in potato tubers

Authors: ROBINSON, BRUCE - Oregon State University; GARCIA, CAROLINA - Technologico De Monterrey; RAMOS, PERLA - Technologico De Monterrey; Bamberg, John; DIAZ DE LA GARZA, ROCIO - Technologico De Monterrey; GOYER, AYMERIC - Oregon State University

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2019
Publication Date: 9/11/2019
Citation: Robinson, B., Garcia, C.S., Ramos, P.P., Bamberg, J.B., Diaz De La Garza, R., Goyer, A. 2019. Expression levels of the y-glutamyl hydrolase I gene predict vitamin B9 content in potato tubers. Agronomy Journal. 9(11):1-16. https://doi.org/10.3390/agronomy9110734.
DOI: https://doi.org/10.3390/agronomy9110734

Interpretive Summary: Folate is such an important vitamin that since 1998 the US has required fortification of basic staples like bread and pasta. That is because folate deficiency affects the nervous system and can have well known catastrophic consequences like spina-bifida in newborns. Less known is the implication of folate insufficiency in mental illness, which affects nearly 1/5 of Americans and costs $192B per year. Most common vegetables are low in folate. Potato is the most consumed vegetable in the US, so would be a promising delivery system for folate if levels in potato could be increased. An attractive approach is breeding the trait of higher folate into new varieties. Fortunately, some wild relatives of potato have very high folate levels. Unfortunately, an impediment to breeding high folate into the crop is that measuring folate content is rather difficult, time-consuming and expensive. We found that the level of a specific enzyme in an individual potato is a good indicator that it also has high folate. Since this enzyme is much easier to measure than folate itself, this discovery should make it much easier to breed for enhanced folate in new potato varieties.

Technical Abstract: Biofortification of folates in staple crops is an important strategy to help eradicate human folate deficiencies. Folate biofortification using genetic engineering has shown great success in rice grain, tomato fruit, lettuce, and potato tuber. However, consumers’ skepticism, juridical hurdles, and lack of economic model have prevented the widespread adoption of nutritionally-enhanced genetically-engineered (GE) food crops. Meanwhile, little effort has been made to biofortify food crops with folate by breeding. Previously we reported >10-fold variation in folate content in potato genotypes. To facilitate breeding for enhanced folate content, we attempted to identify genes that control folate content in potato tuber. For this, we analyzed the expression of folate biosynthesis and salvage genes in low- and high-folate potato genotypes. First, RNA-seq analysis showed that, amongst all folate biosynthesis and salvage genes analyzed, only one gene, which encodes '-glutamyl hydrolase 1 (GGH1), was consistently expressed at higher levels in high- compared to low-folate segregants of a Solanum boliviense accession. Second, quantitative PCR showed that GGH1 transcript levels were higher in high- compared to low-folate segregants for seven out of eight pairs of folate segregants analyzed. These results suggest that GGH1 gene expression is an indicator of folate content in potato tubers.