The vacuolar sugar transporterEarly Response to Dehydration 6-Like4regulates fructose signaling and plant growth

Abstract

Regulation of intracellular sugar homeostasis is maintained by regulation of activities of sugar import and export proteins residing at the tonoplast. We show here that the EARLY RESPONSE TO DEHYDRATION6-LIKE4 protein, being the closest homolog to the proton/glucose symporter ERDL6, resides in the vacuolar membrane. Gene expression and subcellular fractionation studies indicated that ERDL4 was involved in fructose allocation across the tonoplast. Overexpression of ERDL4 increased total sugar levels in leaves, due to a concomitantly induced stimulation ofTST2expression, coding for the major vacuolar sugar loader. This conclusion is supported by the finding thattst1-2knockout lines overexpressingERDL4lack increased cellular sugar levels. ERDL4 activity contributing to the coordination of cellular sugar homeostasis is also indicated by two further observations. Firstly,ERDL4andTSTgenes exhibit an opposite regulation during a diurnal rhythm, and secondly, theERDL4gene is markedly expressed during cold acclimation representing a situation in which TST activity needs to be upregulated. Moreover,ERDL4-overexpressing plants show larger size of rosettes and roots, a delayed flowering time and increased total seed yield. Consistently,erdl4knock-out plants show impaired cold acclimation and freezing tolerance along with reduced plant biomass. In summary, we show that modification of cytosolic fructose levels influences plant organ development and stress tolerance.

Symplasmic phloem loading and subcellular transport in storage roots are key factors for carbon allocation in cassava

“…Conversely, transcripts of proteins involved in vacuolar export such as the H + /sucrose symporter MeSUT4b (Schneider et al, 2012), as well as all three EARLY RESPONSE TO DEHYDRATION 6 ( MeERD6 ) proteins (Kiyosue et al, 1998), and two out of three MeEDL4/ERDL6 orthologs (Poschet et al, 2011) decreased throughout bulking (cluster SR 2 or 3). ERD6 and ERD6-like proteins are part of the MST family and facilitate H + /hexose symport across the tonoplast (Pommerrenig et al, 2018, Khan et al, 2023).…”

“…The MST gene family includes a plethora of genes encoding for proteins involved in tonoplast or plastid transport (Pommerrenig et al, 2018). While transcripts of proteins involved in vacuolar/plastidic import generally increased when cytosolic sugar levels are high, those involved in vacuolar/plastidic export generally decreased in expression under latter conditions (Wormit et al, 2006, Patzke et al, 2018, Klemens et al, 2013, Khan et al, 2023).…”

Carbohydrate distribution via SWEET17 is critical for Arabidopsis inflorescence branching under drought

“…Gene expression data was extracted from RNASeq performed by Khan et al 2022. Therefore, leaf discs from four-week-old Arabidopsis plants were incubated in 3mM MES containing 100mM mannitol, 100mM fructose or 100mM glucose for 24 hours.…”

“…Given that the expression of key factors regulating branching and branch elongation differs between wild types and sweet17 mutant plants, it is reasonable to speculate that fructose, the sole transport substrate of SWEET17 (Chardon et al, 2013), exerts a signaling function in the developmental process of branching. Therefore, to verify this hypothesis we extracted data from RNA-Seq analysis of Arabidopsis wild type leaf discs subjected to mannitol (as control) or fructose (Khan et al, 2022 preprint ). In addition, extracted from the same dataset, we analyzed the effect of glucose, as another abundant monosaccharide, on global gene expression in Arabidopsis.…”

“…RNASeq data was extracted from the dataset created for Khan et al (2022, preprint ). In brief, leaf discs from four-week-old Arabidopsis wild type plants were incubated in 3 mM MES containing 100 mM sugars (mannitol, glucose and fructose) overnight.…”