Modulation of Fructokinase Activity of Potato (Solanum tuberosum) Results in Substantial Shifts in Tuber Metabolism

Abstract

;Potato plants (Solanum tuberosum L. cvs Desiree and Record) transformed with sense and antisense constructs of a cDNA encoding the potato fructokinase StFK1 exhibited altered transcription of this gene, altered amount of protein and altered enzyme activities. Measurement of the maximal catalytic activity of fructokinase revealed a 2-fold variation in leaf (from 90 to 180% of wild type activity) and either a 10-or 30-fold variation in tuber (from 10 or 30% to 300% in Record and Desiree, respectively) activity. The comparative effect of the antisense construct in leaf and tuber tissue suggests that this isoform is only a minor contributor to the total fructokinase activity in the leaf but the predominant isoform in the tuber. Antisense inhibition of the fructokinase resulted in a reduced tuber yield; however, its overexpression had no impact on this parameter. The modulation of fructokinase activity had few, consistent effects on carbohydrate levels, with the exception of a general increase in glucose content in the antisense lines, suggesting that this enzyme is not important for the control of starch synthesis. However, when metabolic fluxes were estimated, it became apparent that the transgenic lines display a marked shift in metabolism, with the rate of redistribution of radiolabel to sucrose markedly affected by the activity of fructokinase. These data suggest an important role for fructokinase, acting in concert with sucrose synthase, in maintaining a balance between sucrose synthesis and degradation by a mechanism independent of that controlled by the hexose phosphate-mediated activation of sucrose phosphate synthase.

Flux Balance Analysis of Barley Seeds: A Computational Approach to Study Systemic Properties of Central Metabolism

“…With respect to the identified essential enzymatic reaction involved in Suc breakdown, antisense inhibition studies document the predominant role of fructokinase in starch metabolism (Davies et al, 2005), thus providing experimental evidence for the model predictions. Antisense inhibition of potato fructokinase resulted in a reduced tuber yield with a substantial shift in tuber metabolism, suggesting an important role for fructokinase in maintaining a balance between Suc synthesis and degradation (Davies et al, 2005).…”

“…Antisense inhibition of potato fructokinase resulted in a reduced tuber yield with a substantial shift in tuber metabolism, suggesting an important role for fructokinase in maintaining a balance between Suc synthesis and degradation (Davies et al, 2005).…”

Untargeted Metabolic Quantitative Trait Loci Analyses Reveal a Relationship between Primary Metabolism and Potato Tuber Quality

“…Gas chromatography-time of flight-mass spectrometry (GC-TOF-MS) has been shown to be useful for the rapid and highly sensitive detection of a large fraction of plant metabolites covering the central pathways of primary metabolism (Roessner et al, 2000;Lisec et al, 2006). In potato, untargeted metabolomic approaches by GC-MS have been successfully applied to assess changes in metabolites under different conditions (Roessner et al, 2000;Urbanczyk-Wochniak et al, 2005), to evaluate the metabolic response to various genetic modifications (Roessner et al, 2001;Szopa et al, 2001; Davies et al, 2005), and to explore the phytochemical diversity among potato cultivars and landraces (Dobson et al, 2008(Dobson et al, , 2009). Additionally, metabolite profiling has been applied to monitor changes during key stages in the tuber life cycle (Davies, 2007).…”

Decreasing the Mitochondrial Synthesis of Malate in Potato Tubers Does Not Affect Plastidial Starch Synthesis, Suggesting That the Physiological Regulation of ADPglucose Pyrophosphorylase Is Context Dependent

“…Imported Suc is cleaved in the cytosol by Suc synthase, resulting in the formation of UDP-Glc and Fru; the UDP-Glc is subsequently converted to Glc-1-P by UDP-Glc pyrophosphorylase. The second product of the Suc synthase reaction, Fru, is efficiently phosphorylated to Fru-6-P by fructokinase (Renz et al, 1993;Davies et al, 2005). Fru-6-P is freely converted to Glc-6-P, in which form it normally enters the amyloplast (Kammerer et al, 1998;Tauberger et al, 2000;Zhang et al, 2008), and once in the plastid, it is converted to starch via the concerted action of plastidial phosphoglucomutase, ADP-Glc pyrophosphorylase (AGPase), and the various isoforms of starch synthase (Martin and Smith, 1995;Geigenberger, 2011).…”