The sunflowers on the cover of New Phytologist 217:1 provide much more than a cheerful picture – they could be vital for human health, explains author Laurent Mène-Saffrané in this guest post about the research behind the cover.
Vitamin E is one of 13 essential vitamins that we need in our diet, since we can’t produce it ourselves. This isoprenoid vitamin is produced exclusively by photosynthetic organisms and plants, especially seed oils extracted from oilseed crops are the main source of vitamin E in the human diet. Vitamin E has been identified as an antisterility factor essential for reproduction in animals; removing vitamin E from the diet of pregnant rats systematically induced miscarriage. The scientific name for vitamin E, tocopherol, derives from this essential property. Two Greek words, tokos, which means offspring, childbirth, and pherein, which means to bring, were coined together and given the suffix ‘–ol’, since it was known that the compound contains an alcohol function.
“Vitamin E is essential for human reproduction and health”
Although the importance of vitamin E for reproduction in rats was established in 1922, its crucial role in human reproduction was demonstrated only recently by a large case-cohort study involving 1605 pregnant women, which shows the strong association between low plasma vitamin E levels in women and the increased rate of miscarriage. The authors showed that vitamin E supplementation is enough to reduce the rate of miscarriage by at least 50%. This is very significant, since independent clinical surveys have clearly established that a large proportion of the human population, including developed countries such as the USA, France, and South Korea, exhibit vitamin E deficiency.
Vitamin E is essential for human reproduction and health. Because we don’t make vitamin E, we must obtain it from our diet, mostly by consuming vegetable oils – one of our main sources. A large proportion of the human population is deficient in vitamin E, which notably increases the risk of miscarriage during pregnancy.
So how is vitamin E made in plants?
Since the late 1990s, several research groups have identified the genes responsible for encoding vitamin E biosynthetic enzymes. Metabolic engineering studies aiming at increasing the vitamin E activity of crops showed that overexpressing vitamin E biosynthetic genes did not significantly increase vitamin E content. In fact, vitamin E biosynthesis is primarily controlled by the amount of vitamin E biosynthetic precursors. The question is: what regulates the amount of vitamin E biosynthetic precursors in plants? Our research aims to identify the genes and metabolic pathways regulating the biosynthesis of vitamin E, and its precursors, in plants – notably in oilseeds.
“Plants that produce more oil produce much less vitamin E”
Using a powerful genetic approach called Forward genetics, we identified the first two genes regulating the accumulation of vitamin E in plants (WRI1 and DGAT1). Both genes are also involved in lipid synthesis and we show that a tradeoff exists between lipid biosynthesis and vitamin E biosynthesis. Using mutants and wild accessions of the genetic model Arabidopsis, we show that plants accumulating more oil produce much less vitamin E.
This could have serious implications for human health and reproduction. To meet the global demand for plant oils, which increased strongly over the last 40 years, plant breeders are favouring new varieties that produce more oil. Our data indicate that this could significantly reduce the amount of vitamin E in plant oils, further limiting its availability for human populations that are already exhibiting vitamin E deficiency.
Sunflower oil is particularly rich in vitamin E – one of its main components is α-tocopherol, the most potent form of vitamin E for humans. It is also one of the most affordable oils sold in supermarkets. The picture above illustrates the importance of regularly consuming plant oils, which contain a lot of nutrients that are essential for human health. The photo shows a sunflower field near the city of Auch in France. This crop is one of the world’s major oilseed crops and its vitamin E content and activity is one of the highest among the main plant oil consumed by humans. The picture was taken with an iPhone 6, edited in Photoshop to remove the clouds in the sky. It is always sunny in the south of France, isn’t it?
Read the paper: Pellaud, S., Bory, A., Chabert, V., Romanens, J., Chaisse-Leal, L., Doan, A. V., Frey, L., Gust, A., Fromm, K. M. and Mène-Saffrané, L. (2017) WRINKLED1 and ACYL-COA:DIACYLGLYCEROL ACYLTRANSFERASE1 regulate tocochromanol metabolism in Arabidopsis. New Phytologist. doi: 10.1111/nph.14856