Rice nicotianamine synthase localizes to particular vesicles for proper function

Abstract

Graminaceous plants release mugineic acid family phytosiderophores to acquire iron from the soil. Recently, we reported that particular vesicles are involved in deoxymugineic acid (DMA) and nicotianamine (NA) biosynthesis and in DMA secretion from rice roots. A fusion protein of rice NA synthase 2 (OsNA S2) and synthetic green fluorescent protein (sGFP) was observed in a dot-like pattern, moving dynamically within the cell. OsNA S2 mutated in the tyrosine motif or di-leucine motif, which was reported to be involved in cellular transport, caused a disruption in vesicular movement and vesicular localization, respectively. Unlike OsNA S2, Arabidopsis NA synthases AtNA S1-4 were distributed uniformly in the cytoplasm with no localization in dot-like structures when transiently expressed in tobacco BY-2 cells. Interestingly, Fe deficiency-inducible genes were upregulated in the OsNA S2-sGFP plants, and the amounts of NA and DMA produced and DMA secreted by the OsNA S2-sGFP plants were significantly higher than in those by the non-transformants and domain-mutated lines. We propose a model for OsNA S2-localized vesicles in rice, and discuss why the introduction of OsNA S2-sGFP caused a disturbance in Fe homeostasis. © 2014 Landes Bioscience.