Plant Biotechnology, Department of Biology, ETH Zurich, Zurich, Switzerland.
Plant Biotechnol J. 2019 Jan;17(1):9-20. doi: 10.1111/pbi.12943. Epub 2018 Jun 12.
Rice, a staple food for more than half of the world population, is an important target for iron and zinc biofortification. Current strategies mainly focus on the expression of genes for efficient uptake, long-distance transport and storage. Targeting intracellular iron mobilization to increase grain iron levels has not been reported. Vacuole is an important cell compartment for iron storage and the NATURAL RESISTANCE ASSOCIATED MACROPHAGE PROTEIN (NRAMP) family of transporters export iron from vacuoles to cytosol when needed. We developed transgenic Nipponbare rice lines expressing AtNRAMP3 under the control of the UBIQUITIN or rice embryo/aleurone-specific 18-kDa Oleosin (Ole18) promoter together with NICOTIANAMINE SYNTHASE (AtNAS1) and FERRITIN (PvFER), or expressing only AtNRAMP3 and PvFER together. Iron and zinc were increased close to recommended levels in polished grains of the transformed lines, with maximum levels when AtNRAMP3, AtNAS1 and PvFER were expressed together (12.67 μg/g DW iron and 45.60 μg/g DW zinc in polished grains of line NFON16). Similar high iron and zinc levels were obtained in transgenic Indica IR64 lines expressing the AtNRAMP3, AtNAS1 and PvFER cassette (13.65 μg/g DW iron and 48.18 μg/g DW zinc in polished grains of line IR64_1), equalling more than 90% of the recommended iron increase in rice endosperm. Our results demonstrate that targeting intracellular iron stores in combination with iron and zinc transport and endosperm storage is an effective strategy for iron biofortification. The increases achieved in polished IR64 grains are of dietary relevance for human health and a valuable nutrition trait for breeding programmes.
水稻是全球一半以上人口的主食，是铁和锌生物强化的重要目标。目前的策略主要集中在表达高效吸收、长距离运输和储存的基因上。针对细胞内铁动员以提高谷物铁含量的策略尚未见报道。液泡是铁储存的重要细胞区室，当需要时，天然抗性相关巨噬蛋白（NRAMP）家族转运蛋白将铁从液泡输出到细胞质。我们开发了在泛素或水稻胚/糊粉层特异性 18 kDa 油蛋白（Ole18）启动子的控制下表达 AtNRAMP3 的转基因日本晴水稻品系，同时表达烟酰胺合成酶（AtNAS1）和铁蛋白（PvFER），或仅表达 AtNRAMP3 和 PvFER。转化系的糙米中铁和锌接近推荐水平，当 AtNRAMP3、AtNAS1 和 PvFER 共同表达时，最大水平（NFON16 系糙米中 12.67μg/g DW 铁和 45.60μg/g DW 锌）。在表达 AtNRAMP3、AtNAS1 和 PvFER 盒的转基因籼稻 IR64 系中也获得了类似的高铁和锌水平（IR64_1 系糙米中 13.65μg/g DW 铁和 48.18μg/g DW 锌），这相当于水稻胚乳中推荐铁含量增加的 90%以上。我们的结果表明，针对细胞内铁库，结合铁和锌的运输和胚乳储存，是铁生物强化的有效策略。在抛光的 IR64 谷物中实现的增加对人类健康具有饮食相关性，是育种计划的一个有价值的营养性状。
