Plant roots can absorb sugars from the rhizosphere, which reduces the consumption of carbon derived from photosynthesis. However, the underlying mechanisms that roots use to control sugar absorption from soil are poorly understood. Here, we identified an apple (Malus × domestica Borkh.) hexose transporter, MdHT1.2, that functions on the root epidermis to absorb glucose (Glc) from the rhizosphere. Based on RNA-seq data, MdHT1.2 showed the highest expression level among 29 MdHT genes in apple roots. Biochemical analyses demonstrated that MdHT1.2 was mainly expressed in the epidermal cells of fine roots and its protein was located on the plasma membrane. The roots of transgenic apple and Solanum lycopersicum lines overexpressing MdHT1.2 had an increased capability to absorb Glc when fed with [13C]-labeled Glc or 2-NBDG, whereas silencing MdHT1.2 in apple showed the opposite results. Further studies established that MdHT1.2-mediated Glc absorption from the rhizosphere changed the carbon assimilate allocation between apple shoot and root, which regulated plant growth. Additionally, a grafting experiment in tomato confirmed that increasing the Glc uptake capacity in the root overexpressing MdHT1.2 could facilitate carbohydrate partitioning to the fruit. Collectively, our study demonstrated that MdHT1.2 functions on the root epidermis to absorb rhizospheric Glc, which regulates the carbohydrate allocation for plant growth and fruit sugar accumulation.

中文翻译：

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苹果 MdHT1.2 介导的根际葡萄糖摄取调节碳水化合物分配


植物根部可以从根际吸收糖分，从而减少光合作用产生的碳的消耗。然而，人们对根部控制土壤糖吸收的基本机制知之甚少。在这里，我们鉴定了一种苹果（Malus × Domestica Borkh.）己糖转运蛋白 MdHT1.2，它在根表皮上发挥作用，从根际吸收葡萄糖 (Glc)。基于RNA-seq数据，MdHT1.2在苹果根部的29个MdHT基因中表现出最高的表达水平。生化分析表明，MdHT1.2主要表达于细根表皮细胞，其蛋白定位于质膜上。当用[13C]标记的Glc或2-NBDG喂养时，过度表达MdHT1.2的转基因苹果和番茄品系的根吸收Glc的能力增强，而在苹果中沉默MdHT1.2则显示相反的结果。进一步的研究表明，MdHT1.2 介导的根际 Glc 吸收改变了苹果芽和根之间的碳同化物分配，从而调节植物生长。此外，番茄嫁接实验证实，增加过表达 MdHT1.2 的根部的 Glc 吸收能力可以促进碳水化合物分配到果实。总的来说，我们的研究表明，MdHT1.2 在根表皮上发挥作用，吸收根际 Glc，调节植物生长和果实糖积累的碳水化合物分配。