Trehalose 6-Phosphate Is Required for the Onset of Leaf Senescence Associated with High Carbon Availability    

Abstract

Trehalose 6-phosphate (T6P) is an important regulator of plant metabolism and development. T6P content increases when carbon availability is high, and in young growing tissue, T6P inhibits the activity of Snf1-related protein kinase (SnRK1). Here, strong accumulation of T6P was found in senescing leaves of Arabidopsis (Arabidopsis thaliana), in parallel with a rise in sugar contents. To determine the role of T6P in senescence, T6P content was altered by expressing the bacterial T6P synthase gene, otsA (to increase T6P), or the T6P phosphatase gene, otsB (to decrease T6P). In otsB-expressing plants, T6P accumulated less strongly during senescence than in wild-type plants, while otsA-expressing plants contained more T6P throughout. Mature otsB-expressing plants showed a similar phenotype as described for plants overexpressing the SnRK1 gene, KIN10, including reduced anthocyanin accumulation and delayed senescence. This was confirmed by quantitative reverse transcriptionpolymerase chain reaction analysis of senescence-associated genes and genes involved in anthocyanin synthesis. To analyze if the senescence phenotype was due to decreased sugar sensitivity, the response to sugars was determined. In combination with low nitrogen supply, metabolizable sugars (glucose, fructose, or sucrose) induced senescence in wild-type and otsA-expressing plants but to a smaller extent in otsB-expressing plants. The sugar analog 3-O-methyl glucose, on the other hand, did not induce senescence in any of the lines. Transfer of plants to and from glucose-containing medium suggested that glucose determines senescence during late development but that the effects of T6P on senescence are established by the sugar response of young plants.In plants, the disaccharide trehalose is synthesized by the conversion of UDP-Glc and Glc-6-P to trehalose 6-phosphate (T6P) in a reaction catalyzed by T6P synthase (TPS), followed by hydrolysis of T6P to trehalose in a reaction catalyzed by T6P phosphatase (TPP). Since the identification of functional TPS and TPP genes in Arabidopsis (Arabidopsis thaliana; Blázquez et al., 1998;Vogel et al., 1998), the role of trehalose metabolism in plants has received increasing attention. Evidence has accumulated suggesting a role for the precursor of trehalose, T6P, as a signal for the regulation of plant metabolism and development (for review, see Eastmond and Graham, 2003;

Comprehensive Dissection of Spatiotemporal Metabolic Shifts in Primary, Secondary, and Lipid Metabolism during Developmental Senescence in Arabidopsis

“…Sugar levels (Glc, Fru, and to some extent Suc) increased during senescence in both the Columbia-0 wild type and T6P phosphatase overexpresssors. Thus, leaf senescence was slowed upon T6P phosphatase overexpression, despite the fact that sugar levels increased, indicating that sugar accumulation alone is not sufficient for the initiation of senescence; instead, sugar signaling during senescence requires T6P (Wingler et al, 2012). This conclusion is supported by the observation that senescence was delayed compared with the wild type when, in T6P phosphatase, overexpresssors were challenged by external sugars.…”

“…T6P has been identified as a signaling molecule for high carbon availability and to be involved in the regulation of a number of developmental processes in plants (Paul et al, 2008;Schluepmann et al, 2012). Of note, a strong (approximately 30-fold) increase of T6P content was recently reported during leaf development and senescence in Arabidopsis leaves; overexpressing a bacterial T6P phosphatase to reduce T6P level in transgenic plants was accompanied by a delay of senescence (Wingler et al, 2012). Sugar levels (Glc, Fru, and to some extent Suc) increased during senescence in both the Columbia-0 wild type and T6P phosphatase overexpresssors.…”

“…However, their roles in senescence remain controversial (Noodén, 1980;Yoshida, 2003;van Doorn, 2004van Doorn, , 2008Wingler et al, 2006Wingler et al, , 2009, since both sugar starvation and addition can induce SAG expression (Gan and Amasino, 1997;Fujiki et al, 2000Fujiki et al, , 2001van Doorn, 2004). Furthermore, although the decline of photosynthesis that occurs during senescence should lead to a decrease of sugar levels, an increase of sugars during senescence was reported in several plant species, including Arabidopsis (Masclaux et al, 2000;Quirino et al, 2001;Stessman et al, 2002;Diaz et al, 2005;Masclaux-Daubresse et al, 2005, 2007Pourtau et al, 2006;Wingler et al, 2006Wingler et al, , 2012. These data are in accordance with the results obtained here in the wholeplant experiment, where we observed an increase of sugar levels in leaves during developmental senescence (Fig.…”

“…Therefore, in order to consider the evidence of specific roles for metabolites in senescence, a more precise analysis of metabolite levels in different tissues and cell types during the process of senescence is required. Although, to date, a number of targeted metabolite profiles, particularly those focused on lipids as seed storage compounds (Yang and Ohlrogge, 2009;Seltmann et al, 2010) and sugars, amino acids, and nutrient ions (Masclaux et al, 2000;Quirino et al, 2001;Stessman et al, 2002;Diaz et al, 2005;Masclaux-Daubresse et al, 2005, 2007Pourtau et al, 2006;Wingler et al, 2006Wingler et al, , 2012, have been generated from maturing and senescing tissues, a broad overview of metabolic changes during senescence, including the interactions between various metabolic pathways, is still lacking. Therefore, we performed a metabolomics study to obtain comprehensive metabolite profiles, including primary and secondary metabolites and lipids, over the course of developmental senescence in rosette leaves before and after bolting and siliques of Arabidopsis in order to investigate the metabolic response and spatiotemporal distribution of metabolites during senescence at the whole-plant level and within single leaves.…”

The Energy-Signaling Hub SnRK1 Is Important for Sucrose-Induced Hypocotyl Elongation

“…For example, tps1 knockout mutants undergo seedling developmental arrest (Gómez et al, 2006), expression of bacterial Tre6P synthase (otsA) or phosphatase (otsB) affects leaf senescence (Wingler et al, 2012), and Tre6P and KIN10 act within a photoperiod-response pathway that controls the induction of flowering (Baena-González et al, 2007;Gómez et al, 2010;Wahl et al, 2013). Signaling by Tre6P and KIN10 is also important for the regulation of growth rates.…”