Tomato tolerance to abiotic stress: a review of most often engineered target sequences

Tomato is one of the most often cultivated vegetable species worldwide. Due to the anti-oxidative and anti-cancer properties of lycopene, tomato consumption as well as production is still increasing. However, its productivity is impaired by a wide range of abiotic stresses, and the establishment of stress-tolerant crops is a key challenge for agricultural biotechnology. Until now, a few genetic approaches have been used to achieve stress tolerance in cultivated tomato plants. Such achievements are based on current knowledge concerning plant adaptation. The presence of adverse environmental factors like extreme temperatures, salinity or drought cause definite biochemical and physiological consequences. Mostly, these are the changes in the metabolic pathways, the expression of stress-inducible genes or the accumulation of low-molecular compounds that play a crucial role in maintaining the plasticity of reactions. The biotechnological methods used to modify tomato to produce upgraded plants are based on introgression of several genes coding enzymes known to mitigate stress or genes contributing to signalling and diverse regulatory pathways. Here, we present an overview of the most often chosen target sequences/molecules that are genetically delivered or engineered to obtain tolerance to environmental constraints. Since adverse conditions cause interrelated stress responses, it is the tolerance molecular players that are consecutively presented in this paper rather than the typically reviewed division of stress types.