Os03g0216700

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Annotated Information

Function

• OsFRDL1 is involved in the translocation of Fe from the roots to the shoots.

Mutation

• In this study, to examine the function and role of OsFRDL1 in rice, the researchers obtained two independent Tos-17 insertion lines; ND8025 (ND) and NC2637 (NC) for this gene. The OsFRDL1 was knocked out in the ND line, but knocked down in the NC line. When the wild-type rice and two Tos-17 insertion lines were grown at 10 mM Fe (as FeSO4), no visible difference was observed among the three lines (Fig. 3A). However, at 0.2 mM Fe, chlorosis was observed in the newly expanded leaves of two Tos-17 lines, but not in the wild type (Fig. 3B). The Fe3+ precipitation in the roots was investigated at 10 mM Fe with Perls blue staining (Green and Rogers, 2004). Fe precipitation was observed in the epidermal cells of the roots of all three lines (Fig. 3, C–E), which was not observed in Arabidopsis roots (Green and Rogers, 2004). This distinct precipitation in rice is attributed to secreted oxygen from rice roots, which oxidizes ferrous iron (Fe2+) into insoluble ferric iron (Fe3+) on the root surface (Horiguchi, 1995). However, there was no difference in the epidermal staining among three lines (Fig. 3, C–E). In contrast, heavy staining was observed in the central vascular part of the knockout line, ND (Fig. 3, D and G), but not in the wild-type line (Fig. 3, C and F). In the knockdown line NC, staining was also observed in the central vascular part (Fig. 3, E and H), although the intensity was not as strong as that of ND.

Figure 3. Phenotype of Tos-17 insertion lines of OsFRDL1. .

• The researchers compared the Fe concentration in the roots and shoots between the wild-type rice and the knockout line (ND). The concentration of Fe in the shoots was significantly lower in the knockout line than in the wild-type rice at either Fe concentration (Fig. 4A). By contrast, the concentration of Fe in the roots was 2 times higher in the knockout line than in the wild-type line at 0.2 mM Fe (Fig. 4B). At 10 mM Fe, the root Fe increased to an extremely high concentration, probably due to precipitation of Fe on the root epidermal layer (Fig. 4C). These results indicate that knockout of OsFRDL1 causes accumulation of Fe in the roots and decreased Fe concentration in the shoots.

Figure 4. Fe concentration in the shoots (A) and roots (B and C). .

• The researchers compared the concentration of Fe and citrate in the xylem sap between ND and wild type at different Fe concentrations in the external solution. The concentration of citrate in the xylem sap of ND was less than one-half that of wild type at either external Fe concentration (Fig. 5A). However, there was no significant difference in malate concentration in the xylem sap between ND and wild type (Fig. 5B). The total Fe concentration in the xylem sap was significantly lower in ND than in wild type (Fig. 5C). In a separate experiment with 10 mM Fe, speciation analysis showed that there was no difference in Fe2+ concentration in the xylem sap between ND and wild type, but the concentration of Fe3+ in ND xylem sap was less than one-half that in wild type (Fig. 5D).

Figure 5. Organic acids and Fe in the xylem sap. .

Labs working on this gene

• Research Institute for Bioresources, Okayama University, Kurashiki 710–0046, Japan