Humans and animals are entirely dependent on dietary intake of vitamins to meet daily requirements, but the edible portions of major staple crops contain insufficient levels to meet this goal. As one example, low levels of specific B vitamins and vitamin E in maize kernels can result in extreme deficiencies in these vitamins when maize is consumed as a staple food, often with devastating health consequences. In developed countries like the US such extreme vitamin deficiencies were mostly eliminated by the mid 20^th century by industrial scale fortification of processed foods, but sections of the population (e.g., the elderly, poor, women of childbearing age and adolescents) still have chronicsuboptimal micronutrient levels that carry long-term negative health consequences. In developing countries, which have infrastructure for large scale fortification of the population, the situation is still dire and > 3billion people suffering from extreme or chronic micronutrient deficiencies. Understanding the molecular genetic basis that determines the levels of individual vitamins in edible portions of major agricultural crops is key to meeting future global needs for food, feed and health. 

The research performed a comprehensive molecular genetic assessment of natural variation for five vitamins present at insufficient levels in kernels of most maize varieties: vitamin E and four B vitamins [thiamine (B1), riboflavin (B2), niacin (B3), pyridoxine (B6)]. The project brought together investigators with diverse skills to apply cutting-edge approaches in high throughput DNA sequencing, genotyping (analysis of different "flavors" of genes), gene expression and phenotyping (analysis of specific compounds in tissues) to identify and understand key genes, among the >30,000 genes in maize, that control accumulation of these vitamins in maize seed. A major outcome of this project has been providing the most detailed understanding to date of the specific genes and alleles (different "flavors" of genes) that affect the synthesis and accumulation of these vitamins. 

For vitamin E we confirmed several previously known genes impacting its levels and identified four new genes, including one that is required for vitamin E synthesis, but which had long eluded researchers. For B vitamins a major outcome was demonstrating that majority of variation in their levels is due to only 1-3 genes each. In some cases (B6), these are known biosynthetic genes while for niacin (B3) it is due to one early-stage biosynthetic gene and another gene encoding a protein that produces the major niacin storage compound in seed, trigonelline, which has no B3 activity. A rare natural variant of this gene that eliminates its activity removes trigonelline from seed which simultaneously increases seed B3 levels by 250%. Trigonelline is the major B3 storage form for most grain crops and this finding should be readily applicable to the other major crops. Finally, for thiamine (B1), we identified a single gene that is responsible for thiamin variation, and demonstrated it encodes a thiamine transporter. Ongoing efforts aim to manipulate this gene to enhance thiamine transport into seed. Another major outcome is that demonstrating that because a very small number of large effect genes control B vitamin levels in seed that simultaneously breeding/engineering increases in B1, B3 and B6 is indeed feasible. Finally, because maize is both a primary food crop and a model for the other major grass crops (wheat, rye, rice, sorghum etc.), the data obtained will serve as both a guide these other major agricultural crops and also be directly transferrable to groups working on maize in both developed and developing countries. 

Last Modified: 11/30/2022
Modified by: Dean Dellapenna