Phytohormonal regulation of root exudation: mechanisms and rhizosphere function
Hawar Sleman Halshoy, Shwana Ahmed Braim, Jawameer R. Hama
Abstract
Root exudates are pivotal mediators of plant-soil interactions, influencing nutrient acquisition, soil structure, microbial community dynamics, and plant health. These exudates comprise primary metabolites, such as sugars, amino acids, and organic acids, as well as secondary metabolites, including flavonoids, phenolics, and alkaloids, along with various enzymes and signaling molecules. Their secretion is tightly regulated by hormones, which orchestrate root development, exudate composition, and adaptive responses to environmental cues. Understanding hormones' role in the root exudation process for plant development and interaction is important; therefore, we aimed to summarize and synthesize recent findings to highlight the roles of major hormones in regulating root exudation, including auxins, cytokinins (CK), gibberellins (GA), abscisic acid (ABA), ethylene, jasmonates (JA), salicylic acid (SA), brassinosteroids (BRs), and strigolactones (SLs). The current understanding summarizes how hormone signaling pathways, crosstalk, and developmental stage transitions modulate exudate profiles, thereby shaping rhizosphere interactions. Particular attention is given to defense-related exudation under biotic and abiotic stress, nutrient mobilization, and the promotion of beneficial microbial associations. The implications of hormone-regulated exudations for sustainable agriculture are discussed, with an emphasis on strategies to enhance nutrient uptake, improve stress resilience, and reduce chemical inputs. Finally, key knowledge gaps are identified, particularly the limited integration of controlled studies with field-based complexity, and the potential for integrating emerging tools, such as hormone-responsive biosensors and metabolomics, to advance agricultural settings is discussed.