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Abstract 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. 

To help high school students develop a deeper understanding of energy and matter flow in biological systems, a key goal of the Next Generation Science Standards (NGSS), we have designed a series of inquiry-driven modules that experimentally explore photosynthesis in the context of carbohydrate partitioning. Carbohydrate partitioning refers to the distribution of photosynthesis products from source organs, such as leaves, to growing or storage tissues. These cost- and time-effective modules help students develop a more integrated understanding of how energy flows from light into leaves before moving outward to other parts of the plant and ultimately into other organisms. Our approach of teaching carbohydrate partitioning along with photosynthesis greatly expands the number of NGSS core ideas and cross-cutting concepts in an integrated manner, empowers students to see how photosynthesis and carbohydrate partitioning are central to their existence, and provides a rich platform for experimentally addressing questions related to photosynthesis, crop production, global climate change, plant physiology, and the carbon cycle.