Tang Zhong, Chen Yi, Chen Fei, Ji Yuchen, Zhao Fang-Jie
State Key Laboratory of Crop Genetics and Germplasm Enhancement, College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing, China.
Department of Metabolic Biology, John Innes Centre, Norwich Research Park, Norwich, UK.
Plant Cell Physiol. 2017 May 1;58(5):904-913. doi: 10.1093/pcp/pcx029.
Rice (Oryza sativa) is a major dietary source of arsenic (As) for the population consuming rice as their staple food. Rice grain contains both inorganic As and methylated As species, especially dimethyarsinate (DMA). DMA is highly mobile in long-distance translocation in plants, but the underlying mechanism remains unknown. In the present study, we showed that OsPTR7 (OsNPF8.1), a putative peptide transporter in rice, was permeable to DMA in Xenopus laevis oocytes. Transient expression of the OsPTR7-green fluorescent protein (GFP) in tobacco protoplasts showed that OsPTR7 was localized in the cell plasma membrane. Quantitative real-time PCR analysis showed that OsPTR7 was more highly expressed in the shoots than in the roots at the seedling stage. At the flowering and grain-filling stage, the OsPTR7 transcript was abundant in the leaves, node I and roots. Knockout or knockdown mutants of OsPTR7 had significantly decreased root to shoot translocation of DMA compared with wild-type plants and accumulated less As in the brown rice. In field-grown plants, DMA accounted for 35% of the total As in the brown rice of wild-type plants but was undetectable in the knockout mutant. Our study demonstrates that OsPTR7 is involved in the long-distance translocation of DMA and contributes to the accumulation of DMA in rice grain.
水稻（Oryza sativa）是将大米作为主食的人群砷（As）的主要饮食来源。稻谷中既含有无机砷，也含有甲基化砷形态，尤其是二甲基砷酸（DMA）。DMA在植物的长距离转运中具有高度流动性，但其潜在机制仍不清楚。在本研究中，我们发现水稻中一种假定的肽转运蛋白OsPTR7（OsNPF8.1）在非洲爪蟾卵母细胞中对DMA具有通透性。OsPTR7-绿色荧光蛋白（GFP）在烟草原生质体中的瞬时表达表明OsPTR7定位于细胞质膜。定量实时PCR分析表明，在幼苗期，OsPTR7在地上部分的表达高于根部。在开花和灌浆期，OsPTR7转录本在叶片、第一节和根部大量存在。与野生型植株相比，OsPTR7的敲除或敲低突变体中DMA从根到地上部分的转运显著减少，糙米中积累的砷也更少。在田间种植的植株中，DMA占野生型植株糙米中总砷含量的35%，但在敲除突变体中未检测到。我们的研究表明，OsPTR7参与DMA的长距离转运，并促进DMA在稻谷中的积累。
