Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2006
Publication Date: 9/23/2006
Citation: Vasconcelos, M., Eckert, H., Arahana, V., Graef, G., Grusak, M.A., Clemente, T. 2006. Molecular and phenotypic characterization of transgenic soybean expressing the arabidopsis ferric chelate reductase gene, FRO2. Planta. 224:1116-1128. Interpretive Summary: Soybean production is reduced under soil conditions that limit the amount of available iron. Iron is an essential nutrient for plants, and when uptake is limited plant growth is reduced, as is the iron content of harvested seeds. Soybean plants can respond to iron-limited conditions by increasing the activity of iron acquisition systems in their roots. This includes a required mechanism, called the iron reductase, that converts ferric iron (Fe3+) to ferrous iron (Fe2+). Ferrous iron is the form absorbed by soybean roots. Unfortunately, many cultivars are unable to fully compensate for iron-limited conditions, and still show signs of iron deficiency. To help make soybean plants more efficient at acquiring iron under limiting conditions, we created a transgenic soybean that contained an extra iron reductase gene to help convert ferric iron to ferrous iron. Root iron reductase activity was ten-fold higher in transgenic plants, relative to control plants. Iron concentrations also were found to be elevated in the transgenic plants when grown under iron-limited conditions. These results are important because they demonstrate that iron deficiency in soybean can be reduced through a biotechnological approach that involves increasing the plant’s root iron reductase activity.
Technical Abstract: Soybean (Glycine max Merr.) production is reduced under iron-limiting calcareous soils throughout the upper Midwest regions of the U.S. Soybean like other dicotyledonous plants responds to iron-limiting environments by induction of an active proton pump, a ferric iron reductase and a Fe 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. Root ferric reductase activity was up to 10-fold higher in transgenic plants and was not subjected to post-transcriptional regulation. The enhanced ferric reductase activity led to reduced chlorosis and increased biomass as compared with control plants grown under hydroponics that mimicked a calcareous soil environment. Iron concentrations in roots and shoots were found to be higher in transgenic plants relative to controls under higher iron treatments. These results suggest that constitutive expression of an iron reductase in soybean can provide a route to alleviate iron deficiency chlorosis.