Transgenic Crops Fortified With Iron, Oxalic Acid, Phytata Like, Iron Storage Protein, Ferriting Synthesis, Translation Level

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Transgenic crops fortified with iron

Iron deficiency is also a serious nutritional problem, affecting an estimated 30% of the world population. Programs involving supplementary food and tablets to overcome iron deficiency are difficult to implement in developing countries, due to the costs involved and due to limited number of health care programs available there.

Although there are some crops like spinach and some leguminous crops that have a relatively higher iron content, they contain oxalic acid and phytate-like substances, which reduce the-bioavailability of iron. In view of this, efforts have been made to develop rice crop, which will allow fortification of iron in the grain with enhanced level of its bioavailability.

For production of transgenic crops that will produce food rich in iron, ferritin (an iron storage protein) has been targeted, which is found in many animals, plants and bacteria. Ferritin consists of as many as 24 subunits that assemble into a large complex (450kDa), that stores upto 4500 iron atoms in its central cavity.

It provides iron for the synthesis of iron proteins like ferredoxin and cytochromes and prevents damage from free radicals that result due to iron-dioxygen interactions. Although, in animals ferritin synthesis is regulated at the translation level, in plants it is regulated at the transcription level.

It has been shown that ferritin can be used by animals as a rich source of iron, so that if iron content in cereal grains is increased, this should solve the problem of dietary iron deficiency. For production of rice crop, having seed fortified with iron, genes for ferritin protein, isolated from soybean and Phaseolus, have been transferred to rice in two independent studies, one conducted in Japan and reported in the year 1999 and the other conducted in Europe, and reported in the year 2001.

A rice variety (IR68144) was developed at IRRI by crossing two varieties, and was rich in Fe and Zn. In 1999, 27 religious sisters used this rice for months and showed an improved iron status. Later, in one of the largest feeding trials of a staple food.

300 nuns from 8 convent schools in the Philippines capital Manila helped in testing it rice anemia, which affected one-third of the world population, in Asia it affected 60% of pregnant women and 40% of school children. About 150 nuns used IR68 144, and other half used the normal rice; a significant difference was observed.

Strategies used for development of high-iron rice

gene constructs used		products in endosperm
(i) ferritin synthase gene from a legume + endosperm specific promoter		ferritin (an Fe rich storage protein)
(ii) overexpression of Oryza MT gene + endosperm specific promoter		cysteine rich proteins (improve Fe absorption)
(iii) heat stable phytase gene from Aspergillus fumigatus + barley glucanase signal peptide for transport to appoplast		chimeric phytase accumulates in apoplast in intact endosperm (degrades endogenous phytic acid which inhibits Fe absorption

MT = metallothionein