Role of Trehalose and Regulation of its Levels as a Signal Molecule to Abiotic Stresses in Plants

Sugars signal the plant cell energy status and trigger proper responses to stresses, also aimed to sustain growth and developmental processes. The ability to sense intracellular sugar levels is of utmost importance for the cell survival. The finely tuned levels of the nonreducing disaccharide trehalose (Tre) and its precursor, trehalose-6-P (T6P), are related to those of sucrose (Suc), whose accumulation is reflected in an increase in T6P levels. T6P in turn inhibits the regulatory protein Snf1-Related protein Kinase-1 (SnRK1), triggering changes in the energy metabolism. Alterations in the Tre/T6P ratios act as a signal leading to several effects on plant metabolic, physiological and developmental processes. The present chapter will deal with the involvement of the Tre/T6P/SnRK1 system in the responses to abiotic stresses. Particular attention will be devoted to hypoxia and cold, in two model plants, i.e., Arabidopsis and rice.