Mutational reconstructed ferric chelate reductase confers enhanced tolerance in rice to iron deficiency in calcareous soil

Iron (Fe) deficiency is a worldwide agricultural problem on calcareous soils with low-Fe availability due to high soil pH. Rice plants use a well documented phytosiderophore-based system (Strategy II) to take up Fe from the soil and also possess a direct [Fe.sup.2+] transport system. Rice plants are extremely susceptible to Iow-Fe supply, however, because of Iow phytosiderophore secretion and Iow [Fe.sup.3+] reduction activity. A yeast [Fe.sup.3+] chelate-reductase gene refre1/372, selected for better performance at high pH, was fused to the promoter of the Fe-regulated transporter, OslRT1, and introduced into rice plants. The transgene was expressed in response to a Iow-Fe nutritional status in roots of transformants. Transgenic rice plants expressing the refre1/372 gene showed higher [Fe.sup.2+] chelate-reductase activity and a higher Fe-uptake rate than vector controls under Fe-deficient conditions. Consequently, transgenic rice plants exhibited an enhanced tolerance to low-Fe availability and 7.9x the grain yield of nontransformed plants in calcareous soils. This report shows that enhancing the [Fe.sup.2+] chelatereductase activity of rice plants that normally have Iow endogenous levels confers resistance to Fe deficiency. ferrous iron | yeast [Fe.sup.2+] chelate reductase | Fe-regulated transporter | transgenic rice