Abscisic Acid (ABA): Biosynthesis, Regulation, and Role in Abiotic Stress Tolerance

Over the past decade, our understanding of plant adaptation to environmental stress, including both fundamental and analytical elements, has grown substantially. The phytohormone abscisic acid (ABA) has a regulatory role in various biochemical and physiological signal transduction cascades in plants. Elevated ABA content is found in plants under multiple abiotic stress conditions such as high salinity and drought. ABA biosynthesis takes place in both plastid and cytosol via an MEP-independent pathway, in which carotene is an intermediate product. ABA is distributed throughout the plant parts where it activates multiple ABA-responsive transcription factors such as bZIP, ABRE, MYB/MYC, NAC, and so on. ABA also interacts with other signaling proteins such as the kinases CPK4, CPK11, SnRK, and OST1. These induced protein kinases activate the expression of ABA-dependent transcription factors such as ABI3, ABFs, and ABI4, and ABI5, which leads to abiotic stress responses. Still, the complexity of ABA-mediated signaling has to be unrevealed in a better way.