Transcription Factors and Environmental Stresses in Plants

Plants are exposed to environmental changes, which are perceived as stresses when they are quick and extreme. Drought, salt, and extreme temperatures, in particular, limit agricultural crop productivity, affecting all stages of plant growth and reproduction, and therefore strongly decreasing crop yield. Worldwide estimates show that most yield loss (70%) can be directly due to abiotic stresses. Moreover, the increasing phenomenon of enthronization and the incorrect use of agricultural land have strongly contributed to land degradation. A large number of abiotic stress-responsive genes have been reported in a variety of plants including Arabidopsis and major crops such as barley, maize, rice, and wheat. Transcriptional control of the expression of these genes is a crucial part of plant response to abiotic stresses. Therefore, recently the transcriptional mechanisms involved in the response to several abiotic stresses have been the subject of intense research, which have been productive in identifying transcription factors (TFs) as important "key or master regulators" of gene expression under stress. An increasing number of TFs have been recently described and essential transcription factor binding regions have been identified for many genes. In fact, these systems of regulation work, thanks to specific cis-elements located in the promoter regions of target genes, which are called regulons. The main regulons that respond to abiotic stresses are DREB1-CBF (dehydration-responsive element binding protein 1/C-repeat binding factor), which is involved in the cold stress response, and DREB2, which acts in ABA-independent gene expression for response to heat and osmotic stress, whereas the ABA-responsive element (ABRE) binding protein (AREB)/ABRE binding factor (ABF) regulon operates in gene expression depending on ABA under osmotic stress. Other regulons, such as MYB/MYC and NAC, induce or repress the expression of genes involved in abiotic stress response. In the last few years, several studies have shown that TFs are powerful tools to engineer enhanced stress tolerance in plants. Therefore, in this chapter, we will summarize the major TFs involved in crop plants' abiotic stress signaling and responses, and the relative plants' adaptive mechanisms at the molecular level. A major finding on molecular mechanisms that occur in stress conditions is the one-way pass for the improvement of stress tolerance in crop plants.