Rice endosperm iron biofortification by targeted and synergistic action of nicotianamine synthase and ferritin

Abstract

SummaryNearly one-third of the world's population, mostly women and children, suffer from iron malnutrition and its consequences, such as anaemia or impaired mental development. Iron fortification of food is difficult because soluble iron is either unstable or unpalatable, and non-soluble iron is not bioavailable. Genetic engineering of crop plants to increase iron content has therefore emerged as an alternative for iron biofortification. To date, strategies to increase iron content have relied on single genes, with limited success. Our work focuses on rice as a model plant, because it feeds one-half of the world's population, including the majority of the iron-malnourished population. Using the targeted expression of two transgenes, nicotianamine synthase and ferritin, we increased the iron content of rice endosperm by more than six-fold.Analysis of transgenic rice lines confirmed that, in combination, they provide a synergistic effect on iron uptake and storage. Laser ablation-inductively coupled plasmamass spectrometry showed that the iron in the endosperm of the transgenic rice lines accumulated in spots, most probably as a consequence of spatially restricted ferritin accumulation. Agronomic evaluation of the high-iron rice lines did not reveal a yield penalty or significant changes in trait characters, except for a tendency to earlier flowering. Overall, we have demonstrated that rice can be engineered with a small number of genes to achieve iron biofortification at a dietary significant level.

Iron Uptake and Loading into Rice Grains

“…Transgenic plants expressing AtNAS1 and Pvferritin simultaneously accumulated six times more Fe in the endosperm than WT plants, showing that this combination exerts a synergistic effect on Fe uptake and storage (Wirth et al 2009). However, a similar approach using HvNAS1 in combination with soybean ferritin did not increase the seed Fe content (Masuda et al 2009).…”

Nutritionally Enhanced Staple Food Crops

“…Thus, NA is a novel and effective promoter of Fe utilization. More importantly, the transgenic rice plants containing AtNAS and Pvferritin genes increased seed-Fe concentration by sixfold, with no yield penalty but such plants were earlier to flower, and that the Fe in the endosperm of the transgenic rice lines accumulated in spots, most probably as a consequence of spatially restricted ferritin accumulation (Wirth et al 2009). Biofortifying rice with NAS alone or in combination with ferritin has great potential in combating global human Fe deficiency in people dependent on rice for their sustenance (Lee et al 2009;Zheng et al 2010).…”

Activation of Rice nicotianamine synthase 2 (OsNAS2) Enhances Iron Availability for Biofortification

“…Transgenic rice grains expressing that gene, driven by the rice actin1 promoter, also have 1.3-fold more iron (Masuda et al, 2009). Targeted expression of Pvferriitn and AtNAS1 improves Fe contents in rice endosperm by more than 6-fold (Wirth et al, 2009). Endosperm-specific expression of OsNAS1 results in a significant rise in NA concentrations in both unpolished and polished grains (Zheng et al, 2010).…”