Evidence for intracellular spatial separation of hexokinases and fructokinases in tomato plants

Abstract

Four hexokinase (LeHXK1-4) and four fructokinase (LeFRK1-4) genes were identified in tomato plants. Previous GFP fusion studies indicate that the gene product of LeHXK3 is associated with the mitochondria while that of LeHXK4 is located within plastids. In this study we found that the enzyme encoded by the fructokinase gene LeFRK3 is also located within plastids. The presence of LeFrk3 enzyme in plastids raises the question of the origin of fructose in these organelles. The other three FRKs enzymes, LeFrk1&2&4, are located in the cytosol. Unlike LeFrk1&2&4, the two additional HXKs, LeHxk1&2, share a common membrane anchor domain and are associated with the mitochondria similar to LeHxk3. The difference in the locations of the cytoplasmic FRK and HXK isozymes suggests that glucose phosphorylation is confined to defined special intracellular localizations while fructose phosphorylation is less confined.

Isozymes of plant hexokinase: Occurrence, properties and functions

“…UniProt entries of HKs are indicated on the left, followed by their AGI numbers or trivial names, some of which were taken from the following references: AtHXK1 and AtHXK2 (Jang et al, 1997), LeHxk1 to LeHxk4 , NtHxk2 (Giese et al, 2005), PpHxk1 and PpHxk2 (Olsson et al, 2003), ScHK2 (Claeyssen et al, 2006), SoHxK1 (Wiese et al, 1999), StHK1 and StHK2 (Veramendi et al, 1999;Veramendi et al, 2002). TargetP (Olsson et al, 2003;Giese et al, 2005;Kandel-Kfir et al, 2006;Damari-Weissler et al, 2006;Cho et al, 2006).…”

Plastidial Thioredoxin z Interacts with Two Fructokinase-Like Proteins in a Thiol-Dependent Manner: Evidence for an Essential Role in Chloroplast Development in Arabidopsis and Nicotiana benthamiana

“…As a control protein, we included FRK3 (At1g66430), an Arabidopsis ortholog of tomato fructokinase 3, which has been shown to be a plastidic fructokinase (German et al, 2004;Damari-Weissler et al, 2006). Whereas enzymatic activity for MBP-AtFRK3 was readily detectable, neither of the two recombinant MBP-FLN fusion proteins showed detectable fructokinase activity (see Supplemental Figure 6 online).…”

Metabolism of soluble sugars in developing melon fruit: a global transcriptional view of the metabolic transition to sucrose accumulation

“…Trees were developed using the public www.phylogeny.fr program(Dereeper et al 2008). Accession numbers of the genes/enzymes presented are a Acid (AAG) and neutral (NAG) a-galactosidases; b Acid (AIN) AAM28822), LeLIN9 (AM050394), LeTIV (M81081); c a and b type neutral invertases according toNonis et al 2008; d UDPglucose epimerases (UGE); Arabidopsis according toBarber et al 2006: AtUGE1 (At1G12780), AtUGE2 (At4G23920), AtUGE3 (At1G63180), AtUGE4 (At1G64440), AtUGE5 (At4G10690); e Sucrose phosphate syntheses (SPS), Arabidopsis according toLutfiyya et al 2007: AtSPS1F (At5G20280), AtSPS2F (At5G11110), AtSPS3F (At1G04920), AtS-PS4F (At4G10120) and citrus: CuSPS1 (AB005023), CuSPS2 (AB006319), CuSPS3 (AB006660); f Cytosolic and plastidic fructokinases (FK), tomato according toDamari-Weissler et al 2006: LeFK1 (U64817), LeFK2 (U64818), LeFK3 (AY323226), LeFK4 (AY099454); g Invertase inhibitors (INH), Arabidopsis: AtC/VIF (At1G47960) AtC/ VIF2 (At5G64620), tobacco: NtCIF (Y12805), NtVIF (Y12806) and tomato LeCIF (AJ010943); h Sucrose synthases (SUS), Arabidopsis according toBieniawska et al 2007: AtSUS1 (At5G20830), AtSUS2 (At5G49190), AtSUS3 (At4G02280), AtSUS4 (At3G43190), AtSUS5 (At5G37180), AtSUS6 (At1G73370) and maize SUS: ZmSUS1 (NP_001105323), ZmSUS2 (NP_001105194), ZmSUS-SH1(NP_00110 5411); i Phosphoglucomutases (PGM), Arabidopsis: AtPGMcyt1 (At1G70730), AtPGMcyt2 (At1G23190), AtPGMpl1 (At5G51820); j Phosphoglucoisomerases (PGI), Arabidopsis: AtPGIcyt (At5G42740), AtPGIpl (At4G24620); k Mitochondrial and plastidic hexokinase (HK) according toKarve et al 2008, Arabidopsis: AtHXK1 (At4G29130), AtHXK2 (At2G19860), AtHXK3 (At1g47840), and ''hexokinase-like'' AtHKL1 (At1G50460), AtHKL2 (At3G20040), AtHKL3 (At4G37840), tomato: LeHK1 (AJ401153), LeHK2 (AF208543), LeHK3 (…”