Protein involved in the abscisic acid (ABA) (5-(1-hydroxy-2,6,6,trimethyl-4-oxocyclohex-2-en-1-y1)-3-methylpenta-2,4-dienoic acid) signaling pathway (e.g. transport and signal transduction) that regulates many aspects of plant growth, development and cellular signaling (e.g. seed dormancy, seed maturation, vegetative growth and responses to various environmental stimuli such as stomatal closure during drought). This phytohormone can be synthesized from farnesyl diphosphate (direct C15 pathway) or from 9-cis-violaxanthine (indirect C40 pathway).