Molecular and phenotypic characterization of transgenic soybean expressing the Arabidopsis ferric chelate reductase gene, FRO2

Abstract

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.

Moving micronutrients from the soil to the seeds: Genes and physiological processes from a biofortification perspective

“…However, for rice, large increases in Zn supply and Zn accumulation in the plant body translated to much smaller increases in seed Zn [221]. Similar observations have been made for Fe supply in wild-type and Fe-overaccumulating mutant pea [11], and transgenic soybean that overexpressed root ferric reductase activity [222]. These results suggest that in some species, the rate limiting steps are downstream of uptake into the plant, and that a strategy to "push" more micronutrient into the plant may not be adequate by itself.…”

Enhanced levels of nicotianamine promote iron accumulation and tolerance to calcareous soil in soybean

“…However, Arabidopsis FRO2-overexpressed soybean exhibited defective growth under normal conditions, while they showed tolerance to Fe deficiency. 47) In rice, the introduction of the mutational reconstructed yeast FRO gene refre1-372 under the control of the OsIRT1 promoter exhibited enhanced tolerance to low Fe availability. 48) It was speculated that the increase in Fe uptake and translocation under Fe deficiency caused by the combined expression of NAS and FRO under the control of an Fe-deficiency-inducible promoter would increase the tolerance of soybean to low Fe availability.…”

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

“…There are some reports obtaining Fe-deficiency tolerance by adding Fe 3ϩ chelate reductase to Strategy I plants, such as tobacco and soybean (17,18). The recent discovery of a direct Fe 2ϩ transport system in rice plants has presented the possibility of obtaining Fe-deficiency tolerance by adding Fe 3ϩ chelate reductase to rice plants, creating a complete Strategy I system.…”