Liquid–liquid phase separation: A new frontier in ABA biosynthesis and signaling, and plant abiotic stress responses

Plants adapt to abiotic stresses through complex signaling networks, in which the phytohormone abscisic acid (ABA) plays a central role. While the core ABA biosynthesis and signaling modules are well characterized, the spatiotemporal mechanisms enabling rapid and specific molecular interactions within crowded cellular environments have remained elusive. This review comprehensively examines the emerging role of liquid–liquid phase separation (LLPS) as a critical physicochemical signal conversion system in plant environmental stress responses. LLPS facilitates the direct regulation of ABA signaling through the formation of biomolecular condensates, such as stress granules and processing bodies, which spatially sequester specific mRNAs and proteins. Key examples include the stabilization of ABA-biosynthetic mRNAs by DRG9 and the dynamic modulation of ABA-responsive transcripts by N6-methyladenosine (m6A) reader proteins SiYTH1 and ECT8. The review also highlights the regulation of stress responses via osmotic stress sensors, such as SEU and DCP5, and extracellular RALF-pectin condensates, which reprogram the transcriptome and integrate with ABA networks. LLPS bridges physical stress detection, such as molecular crowding, with hormonal control and mRNA fate determination, thereby providing plants with rapid, reversible, and spatially compartmentalized adaptive strategies. Finally, we outline future research directions, emphasizing the need to explore phase separation within core ABA components and the potential applications of LLPS in stress-tolerant crop breeding.