Abstract
Carbohydrates, or sugars, regulate various aspects of plant growth through modulation of cell division and expansion. Besides playing essential roles as sources of energy for growth and as structural components of cells, carbohydrates also regulate the timing of expression of developmental programs. The disaccharide trehalose is used as an energy source, as a storage and transport molecule for glucose, and as a stress-responsive compound important for cellular protection during stress in all kingdoms. Trehalose, however, is found in very low amounts in most plants, pointing to a signaling over metabolic role for this non-reducing disaccharide. In the last decade, trehalose-6-phosphate (T6P), an intermediate in trehalose metabolism, has been shown to regulate embryonic and vegetative development, flowering time, meristem determinacy, and cell fate specification in plants. T6P acts as a global regulator of metabolism and transcription promoting plant growth and triggering developmental phase transitions in response to sugar availability. Among the T6P targets are members of the Sucrose-non-fermenting1-related kinase1 (SnRK1) family, which are sensors of energy availability and inhibit plant growth and development during metabolic stress to maintain energy homeostasis. In this review, we will discuss the opposite roles of the sugar metabolite T6P and the SnRK1 kinases in the regulation of developmental phase transitions in response to carbohydrate levels. We will focus on how these two global regulators of metabolic processes integrate environmental cues and interact with hormonal signaling pathways to modulate plant development.
Highlights
As sessile organisms, plants rely heavily on developmental regulation as a mechanism to respond to environmental changes
The tps1 defects could be rescued by expression of the Escherichia coli trehalose-6-phosphate synthase (TPS) gene, but not by trehalose supply, confirming that T6P is essential for embryo development and that it is the lack of T6P and not trehalose that leads to the embryonic phenotype (Eastmond et al, 2002; Schluepmann et al, 2003). These findings indicate that the increase in sugar level at the torpedo stage signals the transition from pattern formation to maturation through T6P, Frontiers in Plant Science | Plant Physiology which regulates cell expansion and the accumulation of storage compounds during maturation (Eastmond et al, 2002; Gómez et al, 2006)
The findings reviewed here show that sugars regulate the timing of developmental phase transitions through T6P and Sucrose-non-fermenting1-related kinase1 (SnRK1) by integrating environmental signals and interacting with hormonal pathways
Summary
Plants rely heavily on developmental regulation as a mechanism to respond to environmental changes. Whereas an animal usually develops a predefined number of organs at predetermined time points, a plant can alter its rate of growth and the number and size of organs in response to endogenous and environmental stimuli at almost any point of its life cycle. In addition to their essential role as energy sources and structural components of cells, carbohydrates play important roles in signaling (Rolland et al, 2006; Eveland and Jackson, 2012; Lastdrager et al, 2014). The mechanism by which T6P regulates growth and development is largely unknown, recent studies have www.frontiersin.org
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