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The yield of maize plants depends on efficient allocation of sucrose from leaves to seeds, which is mediated by the sap-conducting tissue; nown as phloem. The process of translocating photoassimilates into the phloem is; nown as phloem loading, and it is thought to occur by different mechanisms in different species. Phloem loading of sugar has been well characterized in Arabidopsis thaliana (hereafter ‘Arabidopsis’), where it is mediated by a combination of SWEET sucrose effluxers and subsequent upta; e by SUT1/SUC2 H+/sucrose symporters. In maize, ZmSUT1 is a H+/sucrose symporter that actively draws sucrose from the apoplasmic space into the sieve element-companion cell complex (SE-CC), but it had not yet been shown if SWEETs efflux sucrose into the apoplasmic space in maize. Using a combination of single-cell RNA sequencing (scRNA-seq) and classical histological techniques such as in situ hybridization, we determined that a subtype of maize bundle sheath (BS) cell in the ran;-2 intermediate veins shows high and specific expression of sugar and amino acid transporters, including sucrose transporters SWEET13a, b, and c. Therefore, we hypothesized that sucrose is transported from the mesophyll to the abaxial BS cells, where it is then exported to the apoplasm by SWEET13a, b, and c and subsequently ta; en up into the SE-CC by SUT1 for long distance transport. To determine if SWEET13a, b, and c were necessary for phloem loading, we generated triple; noc; out mutants using a multiplexed CRISPR-Cas9 approach, and discovered that the sweet13a, b, c plants were stunted, chlorotic, and accumulated more starch and …