Maternal-to-filial nutrition transfer is central to grain development and yield. nitrate transporter 1/peptide transporter (NRT1-PTR)-type transporters typically transport nitrate, peptides, and ions. Here, we report the identification of a maize (Zea mays) NRT1-PTR-type transporter that transports sucrose and glucose. The activity of this sugar transporter, named Sucrose and Glucose Carrier 1 (SUGCAR1), was systematically verified by tracer-labeled sugar uptake and serial electrophysiological studies including two-electrode voltage-clamp, non-invasive microelectrode ion flux estimation assays in Xenopus laevis oocytes and patch clamping in HEK293T cells. ZmSUGCAR1 is specifically expressed in the basal endosperm transfer layer and loss-of-function mutation of ZmSUGCAR1 caused significantly decreased sucrose and glucose contents and subsequent shrinkage of maize kernels. Notably, the ZmSUGCAR1 orthologs SbSUGCAR1 (from Sorghum bicolor) and TaSUGCAR1 (from Triticum aestivum) displayed similar sugar transport activities in oocytes, supporting the functional conservation of SUGCAR1 in closely related cereal species. Thus, the discovery of ZmSUGCAR1 uncovers a type of sugar transporter essential for grain development and opens potential avenues for genetic improvement of seed-filling and yield in maize and other grain crops.

中文翻译：

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硝酸盐转运蛋白 1/肽转运蛋白家族的糖转运蛋白 ZmSUGCAR1 对于玉米籽粒灌浆至关重要

母体向子代的营养转移对于谷物发育和产量至关重要。硝酸盐转运蛋白 1/肽转运蛋白 (NRT1-PTR) 型转运蛋白通常转运硝酸盐、肽和离子。在这里，我们报告了一种转运蔗糖和葡萄糖的玉米 (Zea mays) NRT1-PTR 型转运蛋白的鉴定。这种糖转运蛋白的活性被命名为蔗糖和葡萄糖载体 1 (SUGCAR1)，通过示踪剂标记的糖摄取和系列电生理学研究（包括非洲爪蟾卵母细胞中的两电极电压钳、非侵入性微电极离子通量估计测定）系统地验证了这种糖转运蛋白的活性。以及 HEK293T 细胞中的膜片钳。ZmSUGCAR1在基底胚乳转移层中特异表达，ZmSUGCAR1的功能缺失突变导致蔗糖和葡萄糖含量显着降低，并随后导致玉米籽粒皱缩。值得注意的是，ZmSUGCAR1 直系同源物 SbSUGCAR1（来自高粱）和 TaSUGCAR1（来自小麦）在卵母细胞中表现出相似的糖转运活性，支持 SUGCAR1 在密切相关的谷物物种中的功能保护。因此，ZmSUGCAR1的发现揭示了一种对谷物发育至关重要的糖转运蛋白，并为玉米和其他谷物作物的种子饱满度和产量的遗传改良开辟了潜在途径。