Tolerance to abiotic stresses in potato plants: a molecular approach

Continuing study of the potato plant's response to stressful conditions has led to the identification of a large number of plant genes whose expression is regulated by external stimuli. Stress-induced genes can be broadly divided into functional or regulatory genes. To the first category belong genes encoding proteins or enzymes of plant metabolic pathway, of molecules involved in repairing cellular damages and/or indispensable for restoring a new cellular homeostasis compatible with the external conditions. The other class includes genes primarily involved in the perception and/or intracellular transduction of the stress signal, such as kinases, phosphatases or transcription factors. The research objectives in the field of plant stress tolerance has recently evolved from a mere cloning and description of stress-induced genes to the design of the best strategy of producing transgenic plants tolerant to environmental constraints. It is well known that stress tolerance is a complex trait, requiring the coordinated regulation of a network of genes that act synergistically and additively. At best, manipulation of one single down-stream gene may contribute only partially to the tolerance of the transgenic plants. Recent studies have shown that it is feasible to regulate the level of expression of many down-stream stress-induced genes in a coordinated fashion by regulating the expression of genes encoding transcription factors able to bind DNA motifs in the promoter of stress-induced genes. However, the constitutive high level of expression of transcription factors often causes detrimental phenotypic effects. This drawback could be by- passed by putting genes for transcription factors under the control of inducible promoters. In this way, endogenous tolerance genes are activated only when the stress event occurs, minimizing the negative pleiotropic effect. Novel technology (reverse genetics, DNA micro- arrays, mRNA differential display, T-DNA tagging, complementation and over-expression of plant cDNA in yeast as model for cellular stress tolerance), improvement of genetic transformation techniques (multiple gene transfer, gene targeting by homologous recombination) as well as a better efficiency of foreign gene expression (discovery of plant promoters with cell-specific, tissue-specific, developmental stage-specific, and/or inducible patterns of expression) will give a tremendous impulse to produce stress tolerant commercial cultivars of the main crops through genetic engineering.