Regulons involved in osmotic stress-responsive and cold stress-responsive gene expression in plants

Many plants, including Arabidopsis thaliana, increase in freezing tolerance in response to low non-freezing temperatures, a phenomenon which is known as cold acclimation. Molecular studies in plants have shown that several genes with various functions are induced by low temperature (cold stress) and osmotic stress such as drought and high salinity. For several stress-inducible genes, cis-acting elements in promoters regions and the corresponding transcription factors that affect the expression of these genes have been analyzed in Arabidopsis. The dehydration-responsive element (DRE)/C-repeat (CRT), cis-acting element, is involved in osmotic stress- and cold stress-inducible gene expression. Transcription factors that bind to the DRE/CRT were isolated and named DRE-binding protein 1 (DREB1)/CRT-binding factor (CBF) and DREB2. The DREB1A/CBF3, DREB1B/CBF1 and DREB1C/CBF2 regulons are involved in cold stress-responsive gene expression, whereas, the DREB2 regulon is involved in osmotic stress-responsive gene expression. In previous experiments, overexpression of the DREB1/CBF genes in transgenic Arabidopsis plants upregulated several stress-inducible genes and increased tolerance to freezing, drought and high-salinity stresses. Subsequent to their discovery, the DREB1/CBF genes have been successfully used to improve abiotic stress tolerance in a number of different crop plants. Interestingly, homologous genes of DREB1/CBF have been found in many other plant species including tomato and rice, which are unable to undergo cold acclimation. Thus, it is apparent that the DREB1/CBF regulon is ubiquitous within higher plants. Current research endeavors are focusing to identify additional transcription factors that are associated with stress response. The ultimate goal of regulon biotechnology is the control of signal transduction networks, a manipulation which in turn is expected to improve stress tolerance in plants.