The abaxial BS cluster contains high levels of mRNAs encoding transport proteins. A, Feature plots show normalized levels of mRNAs for maize genes differentially expressed between the two clusters of bundle sheath cells from data set A plotted in UMAP space. B–F, In situ hybridizations of SWEET13a, SWEET13b, and SWEET13c to localize their mRNAs. Rank-2 intermediate veins from sections hybridized with antisense probes for SWEET13a, SWEET13b, and SWEET13c showed that the mRNA localization of three SWEET13 genes was largely limited to abaxial bundle sheath cells. B and C, SWEET13a mRNA localization was predominantly in abBSCs in the majority of veins (77.5%) and to PP in a subset of veins (22.5%; n = 824). D, No staining was visible after hybridization with the SWEET13a sense probe (negative control). E and F, SWEET13b and SWEET13c probes showed staining predominantly in abBSCs. G, RBCS1 antisense probe hybridized sections showed staining in all BS cells. H, No staining was detected in sections hybridized with an RBCS1 sense probe. I, SUT1 mRNA was localized to a vascular cell which is likely a companion cell in rank-2 intermediate veins (arrow). J, No staining was detected after hybridization with a SUT1 sense probe (negative control). See Supplemental Figure S7 for intermediate rank-1 and major veins. Bars = 100 µm.