Temporal responses of transcripts, enzyme activities and metabolites after adding sucrose to carbon‐deprived Arabidopsis seedlings

Abstract

SummaryArabidopsis seedlings were subjected to 2 days of carbon starvation, and then resupplied with 15 mM sucrose. The transcriptional and metabolic response was analyzed using ATH1 arrays, real-time quantitative (q)RT-PCR analysis of >2000 transcription regulators, robotized assays of enzymes from central metabolism and metabolite profiling. Sucrose led within 30 min to greater than threefold changes of the transcript levels for >100 genes, including 20 transcription regulators, 15 ubiquitin-targeting proteins, four trehalose phosphate synthases, autophagy protein 8e, several glutaredoxins and many genes of unknown function. Most of these genes respond to changes of endogenous sugars in Arabidopsis rosettes, making them excellent candidates for upstream components of sugar signaling pathways. Some respond during diurnal cycles, consistent with them acting in signaling pathways that balance the supply and utilization of carbon in normal growth conditions. By 3 h, transcript levels change for >1700 genes. This includes a coordinated induction of genes involved in carbohydrate synthesis, glycolysis, respiration, amino acid and nucleotide synthesis, DNA, RNA and protein synthesis and protein folding, and repression of genes involved in amino acid and lipid catabolism, photosynthesis and chloroplast protein synthesis and folding. The changes of transcripts are followed by a delayed activation of central metabolic pathways and growth processes, which use intermediates from these pathways. Sucrose and reducing sugars accumulate during the first 3-8 h, and starch for 24 h, showing that there is a delay until carbon utilization for growth recommences. Gradual changes of enzyme activities and metabolites are found for many metabolic pathways, including glycolysis, nitrate assimilation, the shikimate pathway and myoinositol, proline and fatty acid metabolism. After 3-8 h, there is a decrease of amino acids, followed by a gradual increase of protein.

The SUGAR-DEPENDENT1 Lipase Limits Triacylglycerol Accumulation in Vegetative Tissues of Arabidopsis

“…Sugars may also exert an additional effect over substrate provision by enhancing biosynthetic capacity. Increased sugar concentration triggers wide-scale changes in gene expression and enzyme activities in Arabidopsis, many of which are associated with primary metabolism (Bläsing et al, 2005;Osuna et al, 2007). For example, there is evidence that both WRI1 and DGAT1 are induced by sugar (Lu et al, 2003;Masaki et al, 2005).…”

Callose Synthase GSL7 Is Necessary for Normal Phloem Transport and Inflorescence Growth in Arabidopsis

“…This "starvation response" is seen, for example, when the night is extended beyond the normal dawn and in mutants defective in the storage or utilization of starch reserves during the night (Smith and Stitt, 2007). The starvation response can be monitored by measuring transcript levels of genes for which expression is known to be specifically responsive to carbohydrate levels (Gibon et al, 2004;Bläsing et al, 2005;Osuna et al, 2007;Usadel et al, 2008;Graf et al, 2010). We investigated whether the reduced carbohydrate levels in the terminal cluster of flowers and buds of gsl7 inflorescences triggered a starvation response by determining the expression of four starvation-induced genes (At1g76410, At3g59940, At1g08630, and At1g10070) and one sugar-induced gene (At3g13470; Supplemental Table S4).…”

Significance of Light, Sugar, and Amino Acid Supply for Diurnal Gene Regulation in Developing Barley Caryopses

“…Hence, a significant fraction of those genes might act downstream of, or participate in, a sugar-dependent signaling cascade. In Arabidopsis seedlings, more than 4,000 diurnally fluctuating genes are affected by changing Suc levels and many of the rapidly Suc-induced or -repressed genes correlate either positively or negatively to diurnal Suc levels (Blasing et al, 2005;Osuna et al, 2007).…”