Functional regulation of Responsive to abscisic acid (Rab) genes from representative plant species and their stress response

Plants are often subjected to an array of diverse abiotic stresses like high or low temperature, salinity, drought, etc. which tend to alter overall physiology and plant metabolism, causing adverse effects on plant growth, productivity and development, thereby raising issues of food security worldwide. Abiotic stress, being a multigenic trait, exhibits the orchestrated functioning of a wide range of molecular factors. Upon inception of stress, subsequent activation of downstream signalling events, followed by initiation of different stress-responsive mechanisms occur for the re-establishment of cellular homeostasis. One such mechanism is the induction of the abscisic acid (ABA)-inducible gene, Responsive to abscisic acid (Rab), which encodes for hydrophilic proteins belonging to the Group 2 late embryogenesis abundant (LEA) protein that displays protective role by enhancing osmotic stress tolerance. These proteins are also named as dehydrins and are expressed in different plant species during acquisition of desiccation, associated with late stages of embryogenesis. However, these genes have been reported to be induced by salinity, drought, cold and other forms of osmotic stresses in different plant tissues as well. The abscisic acid responsive element (ABRE) is the best characterised cis-element associated with the promoter of Rab genes. The basic leucine zipper (bZIP) transcription factors mostly bind to such ABREs, thereby trans-activating the Rab gene expression. Transgenic plants overexpressing different Rab genes and their associated factors have been reported to generate increased tolerance to different abiotic stresses. Since plant stress tolerance involves regulatory actions of different Rab genes, a detailed overview encompassing the structural and functional aspects of Rab genes in different plant species has been highlighted in the present communication. There is dearth of available review that focuses exclusively on Rab genes as potential candidates of stress tolerance. To our knowledge, this is the only review that provides an exhaustive overview of Rab genes as members of group 2 LEA or dehydrin from diverse plant species with potentiality in abiotic stress responses in plants.