Targeting intracellular transport combined with efficient uptake and storage significantly increases grain iron and zinc levels in rice.

Ting‐Ying Wu,Navreet K Bhullar,Wilhelm Gruissem

doi:10.1111/pbi.12943

Abstract

SummaryRice, a staple food for more than half of the world population, is an important target for iron and zinc biofortification. Current strategies mainly focus on the expression of genes for efficient uptake, long‐distance transport and storage. Targeting intracellular iron mobilization to increase grain iron levels has not been reported. Vacuole is an important cell compartment for iron storage and the NATURAL RESISTANCE ASSOCIATED MACROPHAGE PROTEIN (NRAMP) family of transporters export iron from vacuoles to cytosol when needed. We developed transgenic Nipponbare rice lines expressing AtNRAMP3 under the control of the UBIQUITIN or rice embryo/aleurone‐specific 18‐kDa Oleosin (Ole18) promoter together with NICOTIANAMINE SYNTHASE (AtNAS1) and FERRITIN (PvFER), or expressing only AtNRAMP3 and PvFER together. Iron and zinc were increased close to recommended levels in polished grains of the transformed lines, with maximum levels when AtNRAMP3, AtNAS1 and PvFER were expressed together (12.67 μg/g DW iron and 45.60 μg/g DW zinc in polished grains of line NFON16). Similar high iron and zinc levels were obtained in transgenic Indica IR64 lines expressing the AtNRAMP3, AtNAS1 and PvFER cassette (13.65 μg/g DW iron and 48.18 μg/g DW zinc in polished grains of line IR64_1), equalling more than 90% of the recommended iron increase in rice endosperm. Our results demonstrate that targeting intracellular iron stores in combination with iron and zinc transport and endosperm storage is an effective strategy for iron biofortification. The increases achieved in polished IR64 grains are of dietary relevance for human health and a valuable nutrition trait for breeding programmes.

Highlights

Deficiencies of essential nutrients including iron, zinc, vitamin A, vitamin B-12, riboflavin, vitamin D and vitamin E are common and often coexist in affected populations
NFUN and NFON lines had higher increases in iron concentrations compared to FUN and FON lines, with NFON 12 unpolished grains containing 29.75 lg/ g DW iron (Figure 1b)
All transgenic rice lines had significantly higher iron concentrations in unpolished grains compared to NB grains

Summary

Introduction

Deficiencies of essential nutrients including iron, zinc, vitamin A, vitamin B-12, riboflavin, vitamin D and vitamin E are common and often coexist in affected populations. Supplementation and food fortification are among the recommended approaches to relieve these deficiencies. These approaches are often difficult to implement due to various regional socio-economic factors. The polished white rice (which is mostly the endosperm of the grain) contains mainly starch and is poor in iron, zinc and other micronutrients. Genetic engineering approaches were successful in increasing the iron concentration in polished rice grains (Vasconcelos et al, 2017)

Results

Discussion

Conclusion