Zn-fortified cereal grains in field-grown barley by enhanced root cytokinin breakdown

Abstract

Zinc (Zn) is an essential element in human nutrition. The concentration of Zn in cereals, which is a staple food in developing countries, is often too low thus contributing to Zn malnutrition in nearly two billion people worldwide. We have reported recently that transgenic barley plants expressing a cytokinin-degrading CYTOKININ OXIDASE/DEHYDROGENASE (CKX) gene in their roots form a larger root system and accumulate a higher concentration of Zn in their grains when grown under greenhouse conditions. Here, we have tested this trait under field conditions. Four independent pEPP:CKX lines accumulated an up to 30% higher Zn concentration in their grains as compared to the untransformed control suggesting that this is a stable trait. The increased Zn concentration exceeded the limit set by the HarvestPlus program for wheat. We, therefore, propose that root enhancement achieved by increased degradation of cytokinin in roots can be a sustainable strategy to combat malnutrition caused by Zn deficiency.

Keywords: Barley; Hordeum vulgare; biofortification; cereals; cytokinin; cytokinin oxidase/dehydrogenase; root system architecture; zinc.

Figure 1.

Mineral element concentrations in barley grains. (A) Relative changes in mineral element concentrations in transgenic lines compared to wild type (WT). The concentration of each mineral element in WT grains was set to 100% and relative differences in transgenic lines are shown in a heat map. (B) Concentrations of zinc (Zn) and iron (Fe) in grains of transgenic lines in comparison to WT grains. Four biological replicates for each genotype were analysed, each containing grains from a mix of >100 plants. Bars represent means ±SE. Asterisks indicate significant differences from the WT as determined by as determined by Student t-test (*, p < 0.05; **, p < 0.01, ***, p < 0.001).