Leaf Fructose Content Is Controlled by the Vacuolar Transporter SWEET17 in Arabidopsis

Abstract

In higher plants, soluble sugars are mainly present as sucrose, glucose, and fructose. Sugar allocation is based on both source-to-sink transport and intracellular transport between the different organelles and depends on actual plant requirements. Under abiotic stress conditions, such as nitrogen limitation, carbohydrates accumulate in plant cells. Despite an increasing number of genetic studies, the genetic architecture determining carbohydrate composition is poorly known. Using a quantitative genetics approach, we determined that the carrier protein SWEET17 is a major factor controlling fructose content in Arabidopsis leaves. We observed that when SWEET17 expression is reduced, either by induced or natural variation, fructose accumulates in leaves, suggesting an enhanced storage capacity. Subcellular localization of SWEET17-GFP to the tonoplast and functional expression in Xenopus oocytes showed that SWEET17 is the first vacuolar fructose transporter to be characterized in plants. Physiological studies in planta provide evidence that SWEET17 acts to export fructose out of the vacuole. Overall, our results suggest that natural variation in leaf fructose levels is controlled by the vacuolar fructose transporter SWEET17. SWEET17 is highly conserved across the plant kingdom; thus, these findings offer future possibilities to modify carbohydrate partitioning in crops.

SWEET17, a Facilitative Transporter, Mediates Fructose Transport across the Tonoplast of Arabidopsis Roots and Leaves

“…S12B; data not shown). It is possible that the lower uptake activity mediated by SWEET16 (K m higher than 10 mM measured in an oocyte expression system; Klemens et al, 2013), compared with SWEET17 (K m lower than 10 mM measured in the same oocyte expression system; Chardon et al, 2013), on the tonoplast was below the detection limit due to a high background ( Fig. 6A; Supplemental Fig.…”

“…The T-DNA insertion mutants for SWEET17 (sweet17-1 and sweet17-2; Chardon et al, 2013) and SWEET16 (sweet16-1 and sweet16-2) were obtained from the Salk Institute Genomic Analysis Laboratory (http://signal.salk.edu/ cgi-bin/tdnaexpress): SM_3_15143, as sweet16-1, and SM_3_30077, as sweet16-2.…”

A genome-wide analysis of SWEET gene family in cotton and their expressions under different stresses

“…The mutant of AtSWEET17 plants are dwarfed and have a low seed yield, suggesting that AtS-WEET17 plays a role in the carbon distribution of plants (Chardon et al 2013). OsSWEET14 deletion mutation to the decrease of plant seed size and development delay.…”

“…Other SWEETs have the function of transporting fructose and galactose (Klemens et al 2013;Guo et al 2014;Zhou et al 2014). AtSWEET16 and AtSWEET17 are highly expressed in roots and involved in the transport of monosaccharides and polysaccharides across tonoplast (Klemens et al 2013;Guo et al 2014;Chardon et al 2013). In addition, SWEETs participate in the transport of sugar and ions.…”

Overexpression of the Vacuolar Sugar CarrierAtSWEET16Modifies Germination, Growth, and Stress Tolerance in Arabidopsis

“…In a recent quantitative trait locus analysis, we identified SWEET17 as a novel determinant of leaf Fru content, especially under cold conditions and conditions of low nitrogen supply (Chardon et al, 2013). In fact, a detailed molecular-physiological analysis revealed that SWEET17 is the first vacuole-located SWEET protein and that it serves as a Fru-specific exporter, connecting the vacuolar lumen to the cytosol.…”