Sucrose efflux mediated by SWEET proteins as a key step for phloem transport

Li Qing Chen, Xiao Qing Qu, Bi Huei Hou, Davide Sosso, Sonia Osorio, Alisdair R. Fernie, Wolf B. Frommer

Research output: Contribution to journalArticlepeer-review

Abstract

Plants transport fixed carbon predominantly as sucrose, which is produced in mesophyll cells and imported into phloem cells for translocation throughout the plant. It is not known how sucrose migrates from sites of synthesis in the mesophyll to the phloem, or which cells mediate efflux into the apoplasm as a prerequisite for phloem loading by the SUT sucrose-H+ (proton) cotransporters. Using optical sucrose sensors, we identified a subfamily of SWEET sucrose efflux transporters. AtSWEET11 and 12 localize to the plasma membrane of the phloem. Mutant plants carrying insertions in AtSWEET11 and 12 are defective in phloem loading, thus revealing a two-step mechanism of SWEET-mediated export from parenchyma cells feeding H+-coupled import into the sieve element-companion cell complex. We discuss how restriction of intercellular transport to the interface of adjacent phloem cells may be an effective mechanism to limit the availability of photosynthetic carbon in the leaf apoplasm in order to prevent pathogen infections.

Original languageEnglish (US)
Pages (from-to)207-211
Number of pages5
JournalScience
Volume335
Issue number6065
DOIs
StatePublished - Jan 13 2012
Externally publishedYes

ASJC Scopus subject areas

  • General

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