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Transporting micronutrients more efficiently in rice
A team of researchers led by Navreet Bhullar from the Institute of Molecular Plant Biology at ETH Zurich, Switzerland, have genetically modified one of the most commonly grown varieties of rice. The advantage over the original variety is that these plants are better at mobilising their cellular stores of zinc and iron and depositing in the white part of the rice grain (known as the endosperm). This means that the micronutrients are transported and concentrated there. The ETH researchers are the first to explore this aspect of cellular transport mechanisms of iron and zinc to enrich rice with micronutrients.
To achieve this enrichment, Bhullar and her team incorporated a genetic construct expressing a combination of three additional genes into the rice plants. One of these genes facilitates mobilisation of iron stored in the plant vacuoles, while another encodes for an iron-storing protein, Ferritin, and the third one promotes efficient iron and zinc uptake by the roots.
Last year, the same team of researchers established a proof of concept in combining three nutritionally relevant traits in one rice line. Iron, zinc and β-carotene were increased simultaneously in the rice grains.
High levels of micronutrients achieved
As recommended by the Consultative Group on International Agricultural Research (CGIAR), 15 μg/g dry weight (DW) iron and 28 μg/g DW zinc in polished grains are required to provide 30 per cent of the dietary estimated average requirement (EAR). In their latest work, the ETH researchers developed rice lines with iron increases that bring their iron content up to more than 90 per cent of the recommended iron content, and with up to 170 per cent of the recommended content for zinc in rice grains.
These plants have so far been tested in the lab and under greenhouse conditions. Bhullar will be conducting field experiments in the near future to find out whether the genetically modified rice is also suitable under conditions in the field.
“First we have to confirm that the plants retain similar levels of zinc and iron in the grains under the field conditions. Once we’ve done that, we should assess the bioavailability of these increased nutrients for humans. It could take years before these modified varieties of rice reach the public,” says Bhullar.
The perfect goal for nutrient enrichment
Rice is a staple food for half of the global population. Typically, only the polished grains of rice are eaten. Unfortunately, the most widely grown rice varieties contain just a fraction of many vital nutrients in the grains or lack them altogether. Most of the commercially-bred rice varieties contain only around 2 μg/g iron in the endosperm. This is why micronutrient deficiencies are common in countries where rice provides a major share of the daily calories.
Nearly 1.6 billion people in the world are affected by anaemia, a condition that iron deficiency significantly contributes to. One third of the world’s population have zinc deficiency, which can lead to a compromised immune system.
Rice biofortification is therefore a sustainable approach to improving the health of the affected populations across the globe.
Reference: Wu T-Y, Gruissem W, Bhullar NK. Targeting intra‐cellular transport combined with efficient uptake and storage significantly increases grain iron and zinc levels in rice. Plant Biotechnology Journal, first published: 07 May 2018. doi: 10.1111/pbi.12943
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