Genetic engineering of glycine betaine biosynthesis to enhance abiotic stress tolerance in plants

Glycine betaine (GB) is an important compatible solute that protects plants against the damaging effects of abiotic stresses. A number of plants have been engineered to contain genes of the GB biosynthetic pathway, which confers enhanced tolerance to a range of abiotic stresses during various plant developmental stages. Unlike natural accumulators, the transgenic plants accumulate very low GB concentrations, insignificant in terms of coping with osmotic stress. The GB accumulation in these transgenic plants varies depending upon their capacity for endogenous choline uptake, the type of gene that catalyzes the GB biosynthetic pathway, and the localization of the transgene product in a particular cellular compartment. This review focuses on recent progress in studies of abiotic stress tolerance conferred by GB in transgenic plants.