Characterizing the in vivo role of trehalose in Saccharomyces cerevisiae using the AGT1 transporter

Significance Trehalose is an important molecule for industrial and medical applications. These applications include use as a food additive to increase sweetness and promote freeze-dry preservation. Trehalose is also included in antibody preparations for stabilization during freezing or desiccation. Further, trehalose biosynthesis is required for virulence of fungal pathogens, and, because animal cells do not synthesize trehalose, trehalose biosynthesis is an attractive antifungal target. Despite all of its uses, the direct physiological roles of trehalose remain unclear. Here, we describe the development and characterization of a system in the model yeast Saccharomyces cerevisiae to directly assess the physiological roles of trehalose. We find that many of the roles traditionally ascribed to trehalose are not the result of trehalose accumulation per se. Trehalose is a highly stable, nonreducing disaccharide of glucose. A large body of research exists implicating trehalose in a variety of cellular phenomena, notably response to stresses of various kinds. However, in very few cases has the role of trehalose been examined directly in vivo. Here, we describe the development and characterization of a system in Saccharomyces cerevisiae that allows us to manipulate intracellular trehalose concentrations independently of the biosynthetic enzymes and independently of any applied stress. We found that many physiological roles heretofore ascribed to intracellular trehalose, including heat resistance, are not due to the presence of trehalose per se. We also found that many of the metabolic and growth defects associated with mutations in the trehalose biosynthesis pathway are not abolished by providing abundant intracellular trehalose. Instead, we made the observation that intracellular accumulation of trehalose or maltose (another disaccharide of glucose) is growth-inhibitory in a carbon source-specific manner. We conclude that the physiological role of the trehalose pathway is fundamentally metabolic: i.e., more complex than simply the consequence of increased concentrations of the sugar and its attendant physical properties (with the exception of the companion paper where Tapia et al. [Tapia H, et al. (2015) Proc Natl Acad Sci USA , 10.1073/pnas.1506415112] demonstrate a direct role for trehalose in protecting cells against desiccation).