Department of Plant Sciences

Graminaceous plants including rice (Oryza sativa L.) produce and secrete mugineic acid family phytosiderophores (MAs) to solubilize iron [Fe(III)] in the soil. Vesicles derived from the rough endoplasmic reticulum (rER) observed in Fe-deficient barley roots were suggested to be involved in MA biosynthesis. However, the relationship between these vesicles and MA biosynthesis has not been well characterized. Rice produces and secretes deoxymugineic acid (DMA), a representative member of the MAs. DMA is synthesized from S-adenosylmethionine through three sequential enzymatic reactions catalyzed by nicotianamine synthase (NAS), nicotianamine aminotransferase (NAAT), and deoxymugineic synthase (DMAS). The genes that participate in this pathway have been identified. To investigate the site of DMA biosynthesis in rice, we generated transgenic rice plants expressing OsNAS2 and OsNAAT1 fused to the synthetic green fluorescent protein (sGFP) under the control of their own promoters. We observed sGFP fluorescence in both roots and shoots of OsNAS2-sGFP-transformed rice, but not in those of OsNAAT1-sGFP-transformed rice. In roots, OsNAS2:sGFP was observed in the cortex, epidermis, and root hairs. sGFP fluorescence was also observed in the phloem parenchyma cells of the leaf blade and large vascular bundle. Interestingly, in these cells, OsNAS2:sGFP fluorescence was observed in a dot-like pattern. Confocal laser scanning microscopy of root pericycle cells indicated that the structure with OsNAS2:sGFP dot-like labeling moved dynamically within the cell. Our results indicated that OsNAS2 is localized in these rER-derived vesicles, which have been suggested to be involved in DMA production in rice roots.