Approaches to improving the bioavailability and level of iron in rice seeds

Iron deficiency is estimated to affect about 30% of the world population, m aking iron by far the most deficient nutrient worldwide. Iron supplementati on in the form of tablets and food fortification has not been successful in developing countries, and iron deficiency is still the most important defi ciency related to malnutrition. Here we present experiments that aim to inc rease the iron content in rice endosperm and to improve its absorption in t he human intestine by means of genetic engineering. We first introduced a f erritin gene fi om Phaseolus vulgaris into rice grains, increasing their ir on content up to twofold. To increase iron bioavailability, we introduced a thermotolerant phytase from Aspergillus fumigatus into the rice endosperm. In addition, as cysteine peptides are considered a major enhancer of iron absorption, we overexpressed the endogenous cysteine-rich metallothionein-l ike protein. The content of cysteine residues increased about sevenfold and the phytase level in the grains about 130-fold, giving a phytase activity sufficient to completely degrade phytic acid in a simulated digestion exper iment. However, the fungal protein did not retain its activity after rice c ooking. Therefore a further attempt to specifically reduce the phytic acid in the inner part of the rice endosperm, the tissue eaten after the milling of rice grains, is discussed and biochemical analyses of the transgenic ri ce seeds are now in progress. (C) 2001 Society of Chemical Industry.