Monosaccharide/proton symporter AtSTP1 plays a major role in uptake and response of Arabidopsis seeds and seedlings to sugars

Abstract

The aim of this study was to investigate the in vivo properties and function of the high-af®nity monosaccharide/proton symporter AtSTP1 of Arabidopsis. We isolated an Atstp1 knock-out mutant and found that this plant grows and develops normally. The AtSTP1 gene is expressed in germinating seeds and seedlings, with AtSTP1 activity found mainly in the seedling root. The rate of uptake of [ 14 C]-3-Omethylglucose and [ 14 C]-D-glucose is 60% less in Atstp1 seedlings than in the wild type, showing that AtSTP1 is the major monosaccharide transporter in Arabidopsis seedlings. Transport of D-galactose and D-mannose is also up to 60% less in Atstp1 seedlings compared to wild type, but transport of D-fructose, L-arabinose and sucrose is not reduced. Germination of Atstp1 seed shows reduced sensitivity to D-mannose, demonstrating that AtSTP1 is active before germination. Atstp1 seedlings grow effectively on concentrations of D-galactose that inhibit wild-type growth, even at up to 100 mM D-galactose, indicating that active transport by AtSTP1 plays a major role at very high concentrations of exogenous sugar. These ®ndings provide insight into the physiological function of AtSTP1 and clearly establish its importance in the uptake of extracellular sugars by the embryo and in seedlings.

Pathway of Sugar Transport in Germinating Wheat Seeds

“…Sugar flows into aleurone cells could be amplified by hexose transporters retrieving Glc from the endosperm (Fig. 5; Matsukura et al, 2000;Sherson et al, 2000). However, as described above, aleurone is a net exporter of Suc during germination and Suc levels stored by the time of desiccation can reach concentrations of more than 4% dry weight (see Chrispeels et al, 1973, and refs.…”

“…5) supports the widely held view that Glc produced from starch degradation in the endosperm is taken up by the scutellum, where it is converted to Suc for further translocation (Edelman et al, 1959;Bewley and Black, 1994). For scutella isolated from germinating maize seeds, influx of hexoses appears to occur by passive diffusion (compare with Matsukura et al, 2000;Sherson et al, 2000). In contrast, Suc uptake by isolated maize scutella exhibits behavior consistent with Suc/H 1 symport (Humphreys, 1985).…”

Update on Mechanisms of Plant Cell Wall Biosynthesis: How Plants Make Cellulose and Other (1→4)-β-d-Glycans

“…double those of a CesA; Hong et al, 2001). Plasma membrane hexose and maltose transporters of prokaryotes and eukaryotes are homologous (Maiden et al, 1987), and virtually all of them contain a minimum of 11 to as many as 18 transmembrane spans per functional unit (Reifenberger et al, 1995;Pao et al, 1998;Sherson et al, 2000;Klepek et al, 2010).…”

Sugar transport in arbuscular mycorrhizal symbiosis

“…In Arabidopsis, 14 putative DST genes have been identified and at least seven MST genes can be predicted from the sequences (Williams et al 2000). Many different cDNAs encoding sugar transporters (carriers) in plant tissues not infected with fungi have been identified (Gogarten and Bentrup 1989;Sauer and Tanner 1989;Riesmeier et al 1992;Truernit et al 1996Truernit et al , 1999Sherson et al 2000;Williams et al 2000;Aoki et al 2004;Hackel et al 2006). …”