Sucrose and light regulation of a cold-inducible UDP-glucose pyrophosphorylase gene via a hexokinase-independent and abscisic acid-insensitive pathway in Arabidopsis

Abstract

UDP-glucose pyrophosphorylase (UGPase) is a key enzyme producing UDP-glucose, which is involved in an array of metabolic pathways concerned with, among other functions, the synthesis of sucrose and cellulose. An Arabidopsis thaliana UGPase-encoding gene, Ugp, was profoundly up-regulated by feeding sucrose to the excised leaves and by an exposure of plants to low temperature (5°C). The UGPase activity and its protein content also increased under conditions of sucrose feeding and exposure to cold. The sucrose effect on Ugp was apparently specific and was mimicked by exposure of dark-adapted leaves to light. Drought and O2 deficiency had some down-regulating effects on expression of Ugp. The sugar-signalling pathway for Ugp regulation was independent of hexokinase, as was found by using transgenic plants with increased and decreased expression of the corresponding gene. Subjecting mutants deficient in abscisic acid (ABA) to cold stress conditions had no effect on Ugp expression profiles. Okadaic acid was a powerful inhibitor of Ugp expression, whereas it up-regulated the gene encoding sucrose synthase (Sus1), indicating distinct transduction pathways in transmitting the sugar signal for the two genes in A. thaliana. We suggest that Ugp gene expression is mediated via a hexokinase-independent and ABA-insensitive pathway that involves an okadaic acid-responsive protein phosphatase. The data point towards Ugp as a possible regulatory entity that is closely involved in the homoeostatic readjustment of plant responses to environmental signals.

Genome-Wide Analysis of the Arabidopsis Leaf Transcriptome Reveals Interaction of Phosphate and Sugar Metabolism

“…Tight coupling exists between P i and sugar metabolism and several studies have shown an interaction between sugar metabolism and P i -regulated gene expression (Sadka et al, 1994;Nielsen et al, 1998;Ciereszko et al, 2001aCiereszko et al, , 2001bLejay et al, 2003;FrancoZorrilla et al, 2004;Liu et al, 2005;Mü ller et al, 2005). Such interactions could rely on a secondary effect; for example, sugar added may operate as a scavenger, influencing the level of P i and thereby the expression of any P-regulated gene.…”

“…Feeding P i to excised leaves also decreased the AGPS2 transcript level by antagonizing the induction by Suc (Nielsen et al, 1998). In Arabidopsis, the impact of P on C metabolism has been exemplified by P starvationinduced expression of genes for b-glucosidase (Malboobi and Lefebvre, 1997), UDP-Glc pyrophosphorylase (UGPase), and the small subunit of ADP-Glc pyrophosphorylase (Ciereszko et al, 2001a(Ciereszko et al, , 2001b, and sugar induction of a P i transporter has been demonstrated in Arabidopsis roots (Lejay et al, 2003). Recently, we have shown for Arabidopsis that the sugar-inducible genes encoding b-amylase (BMY1) and chalcone synthase (CHS) are also induced by P deficiency and are more strongly regulated by sugars when leaf segments originate from P-starved plants.…”

“…Aside from the crucial role of P in metabolic pathways (Paul and Stitt, 1993;Plaxton and Carswell, 1999), P status in plants also modifies metabolism by transcriptional regulation of several genes encoding enzymes with function in carbohydrate metabolism (Nielsen et al, 1998;Ciereszko et al, 2001aCiereszko et al, , 2001b. Regulation of gene expression typically represents more long-term metabolic adaptations (Gibon et al, 2004), and sugarregulated gene expression is known to influence general activity of photosynthetic carbon (C) metabolism (Paul and Pellny, 2003;Thum et al, 2004) and a multitude of other aspects of metabolism and tissue development (Rolland et al, 2006).…”

Structure and Dynamics of UDP–Glucose Pyrophosphorylase from Arabidopsis thaliana with Bound UDP–Glucose and UTP

“…The expression of gene At3g03250 is known to be regulated by light as well as phosphate and sucrose concentration [13][14][15] . In addition, in vitro oligomerization of UDPGP has been shown to influence the activity of this enzyme; the most active form being the monomer 16 .…”

Oligomerization, Membrane Association, and in Vivo Phosphorylation of Sugarcane UDP-glucose Pyrophosphorylase

“…In the banana, UGPase genes are up-regulated by ethylene (50), whereas UGPase genes are up-regulated by phosphate deficiency, light exposure, and sucrose supplementation in the potato (51,52). In this study, we evaluated the correlation between the sucrose content and ScUGPase-1 gene expression in the sugarcane cultivars RB855156 (with a higher sucrose content) and RB935744 (with a lower sucrose content), but the ScUGPase-1 profiles were very similar in these cultivars.…”