Soybean (Glycine max Merr.) production is reduced under
iron-limiting calcareous
soils throughout the upper Midwest regions of the US. Like other dicotyledonous plants, soybean responds to
iron-limiting environments by induction of an active
proton pump, a
ferric iron reductase and an
iron transporter. Here we demonstrate that heterologous expression of the Arabidopsis thaliana
ferric chelate reductase gene, FRO2, in transgenic soybean significantly enhances Fe(+3) reduction in roots and leaves. Root
ferric reductase activity was up to tenfold higher in transgenic plants and was not subjected to post-transcriptional regulation. In leaves,
reductase activity was threefold higher in the transgenic plants when compared to control. The enhanced
ferric reductase activity led to reduced
chlorosis, increased
chlorophyll concentration and a lessening in biomass loss in the transgenic events between Fe treatments as compared to control plants grown under hydroponics that mimicked Fe-sufficient and Fe-deficient soil environments. However, the data indicate that constitutive FRO2 expression under non-
iron stress conditions may lead to a decrease in plant productivity as reflected by reduced biomass accumulation in the transgenic events under non-
iron stress conditions. When grown at Fe(III)-
EDDHA levels greater than 10 microM,
iron concentration in the shoots of transgenic plants was significantly higher than control. The same observation was found in the roots in plants grown at
iron levels higher than 32 microM Fe(III)-
EDDHA. These results suggest that heterologous expression of an
iron chelate
reductase in soybean can provide a route to alleviate
iron deficiency chlorosis.