Sucrose Transporter ZmSut1 Expression and Localization Uncover New Insights into Sucrose Phloem Loading.
Sucrose transporters (SUTs) translocate sucrose (Suc) across cellular membranes, and in eudicots, multiple SUTs are known to function in Suc phloem loading in leaves. In maize (Zea mays), the Sucrose Transporter1 (ZmSut1) gene has been implicated in Suc phloem loading based upon RNA expression in leaves, electrophysiological experiments, and phenotypic analysis of zmsut1 mutant plants. However, no previous studies have examined the cellular expression of ZmSut1 RNA or the subcellular localization of the ZmSUT1 protein to assess the gene's hypothesized function in Suc phloem loading or to evaluate its potential roles, such as phloem unloading, in nonphotosynthetic tissues. To this end, we performed RNA in situ hybridization experiments, promoter-reporter gene analyses, and ZmSUT1 localization studies to elucidate the cellular expression pattern of the ZmSut1 transcript and protein. These data showed that ZmSut1 was expressed in multiple cell types throughout the plant and indicated that it functions in phloem companion cells to load Suc and also in other cell types to retrieve Suc from the apoplasm to prevent its accumulation and loss to the transpiration stream. Additionally, by comparing a phloem-mobile tracer with ZmSut1 expression, we determined that developing maize leaves dynamically switch from symplasmic to apoplasmic phloem unloading, reconciling previously conflicting reports, and suggest that ZmSut1 does not have an apparent function in either unloading process. A model for the dual roles for ZmSut1 function (phloem loading and apoplasmic recycling), Sut1 evolution, and its possible use to enhance Suc export from leaves in engineering C3grasses for C4photosynthesis is discussed.
Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri-Columbia, Columbia, Missouri 65211 (R.F.B., K.A.L., N.R.B., M.J.S., D.M.B.).|Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724 (Y.B.-A., T.S., D.J.); and.|Department of Molecular Biology, University of Wyoming, Laramie, Wyoming 82071 (A.L., A.S.).
R Frank
RF
Baker
Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri-Columbia, Columbia, Missouri 65211 (R.F.B., K.A.L., N.R.B., M.J.S., D.M.B.).|Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724 (Y.B.-A., T.S., D.J.); and.|Department of Molecular Biology, University of Wyoming, Laramie, Wyoming 82071 (A.L., A.S.).
Kristen A
KA
Leach
Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri-Columbia, Columbia, Missouri 65211 (R.F.B., K.A.L., N.R.B., M.J.S., D.M.B.).|Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724 (Y.B.-A., T.S., D.J.); and.|Department of Molecular Biology, University of Wyoming, Laramie, Wyoming 82071 (A.L., A.S.).
Nathanial R
NR
Boyer
Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri-Columbia, Columbia, Missouri 65211 (R.F.B., K.A.L., N.R.B., M.J.S., D.M.B.).|Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724 (Y.B.-A., T.S., D.J.); and.|Department of Molecular Biology, University of Wyoming, Laramie, Wyoming 82071 (A.L., A.S.).
Michael J
0000-0001-9537-7393
MJ
Swyers
Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri-Columbia, Columbia, Missouri 65211 (R.F.B., K.A.L., N.R.B., M.J.S., D.M.B.).|Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724 (Y.B.-A., T.S., D.J.); and.|Department of Molecular Biology, University of Wyoming, Laramie, Wyoming 82071 (A.L., A.S.).
Yoselin
0000-0001-9779-0413
Y
Benitez-Alfonso
Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri-Columbia, Columbia, Missouri 65211 (R.F.B., K.A.L., N.R.B., M.J.S., D.M.B.).|Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724 (Y.B.-A., T.S., D.J.); and.|Department of Molecular Biology, University of Wyoming, Laramie, Wyoming 82071 (A.L., A.S.).
Tara
T
Skopelitis
Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri-Columbia, Columbia, Missouri 65211 (R.F.B., K.A.L., N.R.B., M.J.S., D.M.B.).|Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724 (Y.B.-A., T.S., D.J.); and.|Department of Molecular Biology, University of Wyoming, Laramie, Wyoming 82071 (A.L., A.S.).
Anding
0000-0002-2603-8854
A
Luo
Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri-Columbia, Columbia, Missouri 65211 (R.F.B., K.A.L., N.R.B., M.J.S., D.M.B.).|Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724 (Y.B.-A., T.S., D.J.); and.|Department of Molecular Biology, University of Wyoming, Laramie, Wyoming 82071 (A.L., A.S.).
Anne
0000-0001-7282-4189
A
Sylvester
Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri-Columbia, Columbia, Missouri 65211 (R.F.B., K.A.L., N.R.B., M.J.S., D.M.B.).|Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724 (Y.B.-A., T.S., D.J.); and.|Department of Molecular Biology, University of Wyoming, Laramie, Wyoming 82071 (A.L., A.S.).
David
D
Jackson
Division of Biological Sciences, Interdisciplinary Plant Group, and Missouri Maize Center, University of Missouri-Columbia, Columbia, Missouri 65211 (R.F.B., K.A.L., N.R.B., M.J.S., D.M.B.); braundm@missouri.edu.|Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724 (Y.B.-A., T.S., D.J.); and braundm@missouri.edu.|Department of Molecular Biology, University of Wyoming, Laramie, Wyoming 82071 (A.L., A.S.) braundm@missouri.edu.
David M
DM
Braun
D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D017930:Genes, Reporter; D017403:In Situ Hybridization; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D052585:Phloem / Q000378:metabolism*; D018515:Plant Leaves / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D030821:Plants, Genetically Modified; D014176:Protein Biosynthesis; D021381:Protein Transport; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D012098:Reproduction / Q000235:genetics; D013395:Sucrose / Q000378:metabolism*; D014158:Transcription, Genetic; D019076:Transgenes; D003313:Zea mays / Q000235:genetics* / Q000378:metabolism*
D026901:Membrane Transport Proteins; D010940:Plant Proteins; D018749:RNA, Plant; C078729:sucrose transport protein, plant; D013395:Sucrose