Analysis of Transport Activity of Arabidopsis Sugar Alcohol Permease Homolog AtPLT5

Abstract

The transporters responsible for sugar uptake into non-photosynthetic sink tissues in plants, such as roots and flowers, have not been fully identified and analyzed. Plants encode around 100 putative sugar transporters within the major facilitator superfamily, yet only a few have been studied. Here we report the analysis of a sugar alcohol permease homolog (AtPLT5, At3g18830) from Arabidopsis. A wide range of sugars including hexoses, pentoses, tetroses, a sugar acid, and sugar alcohols but not disaccharides induced inward currents in oocytes expressing AtPLT5. AtPLT5 expression also resulted in 14 C-labeled substrate uptake in oocytes, indicating that AtPLT5 encodes an ion-coupled uptake transporter. K 0.5 values for glucose and sorbitol were highly dependent on external pH. Expression of AtPLT5 was found primarily in sink tissues: in the elongation zone of roots, in the inflorescence stem, and several floral structures, especially in the floral abscission zone. Expression was induced by mechanical wounding and insect feeding. Analysis of transport properties and expression in Arabidopsis indicate that AtPLT5 functions to transport a wide range of sugars into specific sink tissues in the plant.Most plant cells are connected by plasmodesmata, forming multicellular "symplasmic domains" (1) that allow exchange of small metabolites between cells. Transporters in the plasma membrane are required for transmembrane metabolite uptake into specific cell types, such as guard cells, pollen cells, and the sieve element/companion cell (SE/CC) complex that are symplasmically isolated. In addition, symplasmic domains of sink cells, for example, in fruit (2), require metabolite uptake transporters to support growth and development (for review, see Ref.3). Furthermore, events such as wounding, dehiscence, or programmed cell death will release metabolites into the cell wall space, and it is expected that surrounding cells have the capability to take up the released compounds.Although not yet functionally characterized, specific sugar transporter homologs are expressed during senescence (4), dehydration (5, 6), or pathogen attack (7) and may function in metabolite uptake. Arabidopsis encodes a wide array of metabolite transporters, around 100 potential metabolite transporters within the major facilitator superfamily (MFS) 1 alone. Available sequence data indicates that a similar situation exists in other plant species as well. Aside from the well characterized STP family of hexose transporters (8), very little information is available concerning transport activity of plant MFS members.Within the MFS, Arabidopsis encodes three groups of transporters that are closely related to the inositol permeases ITR1 and ITR2 from Schizosaccharomyces pombe (9) and Saccharomyces cerevisiae (10) and the xylose permease from Lactobacillus brevis (11). One group of four genes contains AtpGlcT (At5g16150), the plastidic glucose translocator (12). A second group of four genes is most similar to the plant vacuolar inositol permeases (Mitr1 and Mitr2)...

Functional Analysis of an Arabidopsis thaliana Abiotic Stress-inducible Facilitated Diffusion Transporter for Monosaccharides

“…Its K m value was exceptionally high and showed lower affinity to glucose (Fig. 4D) compared with previously characterized sugar transporters such as STP1 (about 20 M) (13), PLT5 (about 2 mM) (14,41), or VGT1 (about 4 mM) (15). Moreover, the transport activity of ESL1(LLL/AAA) was not affected by the reduction of the proton gradient caused by a protonophore (Table 1), thereby indicating that ESL1 is a facilitated diffusion transporter.…”

Cloning and expression analysis of PpSUT2 encoding a sucrose transporter in pear

“…Plant SUT2 proteins are believed to function as signal proteins that control the transport of sucrose across membranes Schulze et al, 2000;Reinders et al, 2005) by sensing sucrose signals that directly regulate the expression, folding, and activities of SUT1 and SUT4. This regulates the sucrose content of plant fruit Weise et al, 2000).…”

The plasma membrane proteome of Medicago truncatula roots as modified by arbuscular mycorrhizal symbiosis

“…In Arabidopsis, its closest homologue, AtPLT5, corresponds to a polyol transporter located in the PM that mediates H + -symport of myo-inositol, glycerol, and ribose (Klepek et al 2005). AtPL5 notably is believed to provide sink tissues with a range of carbohydrates known to be present in the phloem and assumed to be transported into sink cells (Reinders et al 2005). NSAF values also show the induction in AM roots of the mycorrhiza-specific peptide nitrate/transporter PTR1 and the sugar transport protein 13 (PT13).…”