ABA as a Universal Plant Hormone

Abstract

Abscisic acid (ABA) is a sesquiterpene known to regulate environmental stress responses in angiosperms, such as water-loss-induced stomatal closure, development of seed desiccation tolerance during maturation, and salt-, desiccation-, and freezing-stress tolerance of vegetative tissues. An ABA-induced increase in stress tolerance is also reported in other land plant lineages, including nonvascular bryophytes that diverged from vascular plants more than 420 million years ago. Thus, it is hypothesized that acquisition of sensing and response mechanisms for ABA by land plant ancestors was critical for invasion of and adaptation to land. Because bryophytes are key organisms in plant evolution, clarification of their ABA-dependent processes is important for understanding land plant evolutionary adaptation. Based on past and current studies on ABA in non-seed plants and phylogenetic analysis of genome information from various plant species, we discuss the evolution of ABA function and biosynthesis, transport, and signaling network pathways as well as calcium signaling because of its importance in ABA signaling in angiosperms. Future directions of ABA research in the evo-devo field are also discussed.