, Volume 217, Issue 3, pp 483–489 | Cite as

Protein phosphorylation plays a key role in sucrose-mediated transcriptional regulation of a phloem-specific proton–sucrose symporter

  • Wendy D. Ransom-Hodgkins
  • Matthew W. Vaughn
  • Daniel R. Bush
Original Article


Assimilate partitioning refers to the systemic distribution of sugars and amino acids from sites of primary assimilation (source tissue) to import-dependent tissues and organs (sinks). One of the defining questions in this area is how plants balance source productivity with sink demand. Recent results from our laboratory showed that sucrose transport activity is directly proportional to the transcription rate of the phloem-specific proton–sucrose symporter BvSUT1 in Beta vulgaris L. Moreover, symporter gene transcription is regulated by sucrose levels in the leaf. Here we show that sucrose-dependent regulation of BvSUT1 transcription is mediated, at least in part, by a protein phosphorylation relay pathway. Protein phosphatase inhibitors decreased sucrose transport activity, symporter protein and mRNA abundance, and the relative transcription rate of the symporter gene. In contrast, protein kinase inhibitors had no effect or increased sucrose transport, protein and mRNA abundance, and transcription. Furthermore, pre-treating leaves with kinase inhibitors before feeding with sucrose blocked the sucrose-dependent decrease in symporter transcription and transport activity. The latter observation provides direct evidence for a protein phosphorylation cascade operating between the sucrose-sensor and the transcriptional regulator that controls BvSUT1 expression and, ultimately, phloem loading.


Beta Okadaic acid Protein phosphorylation Sucrose transporter 



protein kinase C


proton motive force


plasma membrane vesicle



This research was supported by grants from the U.S. Department of Agriculture–Agricultural Research Service and the U.S. Department of Energy, Energy Biosciences.


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Copyright information

© Springer-Verlag 2003

Authors and Affiliations

  • Wendy D. Ransom-Hodgkins
    • 1
  • Matthew W. Vaughn
    • 2
    • 4
  • Daniel R. Bush
    • 1
    • 2
    • 3
  1. 1.Department of Plant Biology, 190 E.R. Madigan LaboratoryUniversity of Illinois at Urbana–ChampaignUrbanaUSA
  2. 2.Program in Physiological and Molecular Plant Biology, 190 E.R. Madigan LaboratoryUniversity of Illinois at Urbana–ChampaignUrbanaUSA
  3. 3.Photosynthesis Research Unit, USDA–ARS, 190 E.R. Madigan LaboratoryUniversity of Illinois at Urbana–ChampaignUrbanaUSA
  4. 4.Cold Spring Harbor LaboratoryCold Spring HarborUSA

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