Abscisic Acid-Mediated Drought Tolerance in Populus: Physiological, Molecular, and Biotechnological Perspectives

Drought stress is a major constraint on global forestry productivity and poses a significant threat to economically important tree species such as Populus. Abscisic acid (ABA) signaling plays a central role in drought tolerance by regulating molecular, physiological, and biochemical processes. This review summarizes current knowledge of ABA signaling pathways and their roles in drought resilience in Populus. It covers physiological responses, molecular regulatory networks, hormonal crosstalk, biotechnological advances, and emerging field applications. Core ABA signaling components, including PYR/PYL/RCAR receptors, PP2Cs, SnRK2 kinases, and transcription factors such as ABFs, NACs, and MYBs, coordinate adaptive responses involved in stomatal regulation, osmotic adjustment, and root system remodeling. Integrative omics approaches, like transcriptomics, proteomics, metabolomics, and epigenomics, have provided mechanistic insights into ABA-mediated drought responses, although some regulatory mechanisms are supported by conserved evidence from model plants and require further validation in Populus. Recent biotechnological advances, including gene overexpression, RNA interference (RNAi), CRISPR/Cas9 genome editing, and emerging CRISPR-based regulatory approaches, provide new opportunities for manipulating ABA-associated drought responses in Populus. While several genome-editing and genetic approaches have been experimentally validated in Populus, many ABA-related targets remain prospective strategies requiring further functional evaluation. However, practical implementation remains limited by an incomplete understanding of hormonal crosstalk, insufficient characterization of epigenetic regulation, and ecological and social concerns. Addressing these challenges requires ecological trials, deeper analyses of hormone networks, advanced epigenetic research, robust environmental risk assessments, and interdisciplinary integration. Future progress will depend on linking molecular discoveries with physiological validation and long-term field evaluation to develop drought-resilient Populus cultivars for sustainable forestry under changing climate conditions.