Isolation and characterization of two fructokinase cDNA clones from rice

A full-length coding domain sequence of a gene analogous to granule-bound starch synthase (GBSS; ADP-glucose-starch glucosyltransferase, EC 2.4.1.21) was cloned and defined as OsGBSSII based on a Nitrogen (N)-starvation-induced cDNA library constructed using the rapid subtraction hybridization method. The deduced amino acid sequence of OsGBSSII was 62-85% identical to those of GBSS proteins from other plant species. The exon/intron organization of OsGBSSII was similar to that of OsGBSSI. OsGBSSII was mainly expressed in leaves and its protein was exclusively bound to starch granules in rice leaves, which suggests that the amylose in rice leaves is synthesized by OsGBSSII. N-starvation-induced expression of OsGBSSII could be repressed by supplying nitrate, ammonia or amino acid (glutamic acid or glutamine), glucosamine (an inhibitor of hexokinase) or dark conditions. These results indicate that N-starvation induction was dependent on the photosynthetic product and hexokinase in rice leaves. Sugars induced the accumulation of OsGBSSII transcripts in excised leaves through glycolysis-dependent pathways. OsGBSSII gene expression is regulated by the circadian rhythm in rice leaves.

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“…Hybridization was carried out as described previously (Jiang et al 2003a). For RT-PCR, the cDNA was reverse-transcribed from 2 lg of total RNA.…”

Section: Rna Gel Blot and Rt-pcr Analysismentioning

confidence: 99%

Cloning and characterization of the granule-bound starch synthase�II gene in rice: gene expression is regulated by the nitrogen level, sugar and circadian rhythm

Dian

Jiang

Chen

et al. 2003

Planta

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“…Biochemical and/or molecular studies have identified hexokinases in many plant species (Ca´rdenas et al 1998;Dai et al 1999;Guglielminetti et al 2000;Jiang et al 2003). Arabidopsis has two hexokinase genes and four hexokinase-like genes (Dai et al 1999;.…”

Section: Introductionmentioning

confidence: 99%

Structure, expression, and functional analysis of the hexokinase gene family in rice (Oryza sativa L.)

Cho

Ryoo

et al. 2006

Planta

135

146

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Hexokinase (HXK) is a dual-function enzyme that both phosphorylates hexose to form hexose 6-phosphate and plays an important role in sugar sensing and signaling. To investigate the roles of hexokinases in rice growth and development, we analyzed rice sequence databases and isolated ten rice hexokinase cDNAs, OsHXK1 (Oryza sativa Hexokinase 1) through OsHXK10. With the exception of the single-exon gene OsHXK1, the OsHXKs all have a highly conserved genomic structure consisting of nine exons and eight introns. Gene expression profiling revealed that OsHXK2 through OsHXK9 are expressed ubiquitously in various organs, whereas OsHXK10 expression is pollen-specific. Sugars induced the expression of three OsHXKs, OsHXK2, OsHXK5, and OsHXK6, in excised leaves, while suppressing OsHXK7 expression in excised leaves and immature seeds. The hexokinase activity of the OsHXKs was confirmed by functional complementation of the hexokinase-deficient yeast strain YSH7.4-3C (hxk1, hxk2, glk1). OsHXK4 was able to complement this mutant only after the chloroplast-transit peptide was removed. The subcellular localization of OsHXK4 and OsHXK7, observed with green fluorescent protein (GFP) fusion constructs, indicated that OsHXK4 is a plastid-stroma-targeted hexokinase while OsHXK7 localizes to the cytosol.

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“…Although several gene functional studies have been carried out to assess the role of hexokinase, to date the majority of assessments of plant FKs have been carried out in heterologous expression systems (Kanayama et al 1998;Jiang et al 2003, Zhang et al 2003. The exception to this statement is the analysis of FKs from tomato, performed in some detail by Bennett and co-workers (Kanayama et al 1998, Dai et al 2002a, Odanaka et al 2002, German et al 2003.…”

Section: Introductionmentioning

confidence: 99%

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

Davies¹,

Shepherd²,

Burrell

et al. 2005

Plant and Cell Physiology

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;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.

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Isolation and characterization of two fructokinase cDNA clones from rice

Cited by 45 publications

References 19 publications

Cloning and characterization of the granule-bound starch synthase�II gene in rice: gene expression is regulated by the nitrogen level, sugar and circadian rhythm

Cloning and characterization of the granule-bound starch synthase�II gene in rice: gene expression is regulated by the nitrogen level, sugar and circadian rhythm

Structure, expression, and functional analysis of the hexokinase gene family in rice (Oryza sativa L.)

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

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