Naoki Yamaji, Yuma Takemoto, Takaaki Miyaji, Namiki Mitani-Ueno, Kaoru T. Yoshida & Jian Feng Ma

NATURE 92, Vol. 541, January 5 2017; doi:10.1038/nature20610

ABSTRACT

Phosphorus is an important nutrient for crop productivity. More than 60% of the total phosphorus in cereal crops is finally allocated into the grains and is therefore removed at harvest. This removal accounts for 85% of the phosphorus fertilizers applied to the field each year 1, 2. However, because humans and non-ruminants such as poultry, swine and fish cannot digest phytate, the major form of phosphorus in the grains, the excreted phosphorus causes eutrophication of waterways. A reduction in phosphorus accumulation in the grain would contribute to sustainable and environmentally friendly agriculture. Here we describe a rice transporter, SULTR-like phosphorus distribution transporter (SPDT), that controls the allocation of phosphorus to the grain. SPDT is expressed in the xylem region of both enlarged- and diffuse-vascular bundles of the nodes, and encodes a plasma-membrane-localized transporter for phosphorus. Knockout of this gene in rice (Oryza sativa) altered the distribution of phosphorus, with decreased phosphorus in the grains but increased levels in the leaves. Total phosphorus and phytate in the brown de-husked rice were 20–30% lower in the knockout lines, whereas yield, seed germination and seedling vigour were not affected. These results indicate that SPDT functions in the rice node as a switch to allocate phosphorus preferentially to the grains. This finding provides a potential strategy to reduce the removal of phosphorus from the field and lower the risk of eutrophication of waterways.

See: http://www.nature.com/nature/journal

Figure 1: Tissue specificity of SPDT expression and subcellular localization of SPDT. a–h, Tissue specificity of SPDT expression in nodes. Immunostaining with an anti-green fluorescent protein (GFP) antibody was performed in basal node (a–c) and node I (d–h) of transgenic rice carrying SPDT promoter-GFP (a, b, d–g) and of wild-type rice (c, h). Images are representative of eight independent lines. Boxed areas in  a, d and e are magnified in b, e, f and g, respectively. Fluorescence from the secondary antibody (red) and the cell wall auto-fluorescence (blue) are shown. Areas of enlarged vascular bundles (EVBs) and diffuse vascular bundles (DVBs) are indicated by yellow dashed lines in e. The xylem and phloem regions of regular vascular bundles (x and p), enlarged vascular bundles (xE and pE), and diffuse vascular bundles (xD and pD) are shown. i–l, Subcellular localization of SPDT. SPDT:GFP was transiently introduced into onion epidermal cells together with DsRed by particle bombardment. Fluorescence signals from GFP (i), DsRed (j) and the merged images (k) are shown. The boxed area in k is magnified in l. Images are representative of three independent cells. Scale bars, 100 μ  m.