Molecular mechanisms of root expansion in medicinal plants

Medicinal plants with storage root expansion play essential roles in food supply, disease prevention, and therapeutic applications. Storage-root enlargement is a highly coordinated developmental process involving primary root specialization, secondary growth, and organ-specific differentiation. Recent studies have revealed that endogenous phytohormones, including auxin, cytokinin, gibberellin, abscisic acid, and jasmonic acid, regulate this process through interconnected signaling pathways that control cell division, cambial activity, and radial growth. Transcription factors such as the ARF, AUX/IAA, NAC, and PLT families function as central regulatory nodes that integrate hormonal and environmental signals. These regulatory networks modulate lignin deposition, carbohydrate metabolism, and secondary meristem activity. These coordinated processes ultimately drive structural remodeling and functional differentiation during root enlargement. Environmental factors, including temperature, CO₂ concentration, nutrient availability, water status, and rhizosphere1830107 microbial communities, further influence these molecular pathways by reshaping hormone balance, assimilate allocation, and root developmental programs. Despite recent progress, the core regulatory modules and species-specific mechanisms underlying storage-root enlargement in medicinal plants remain poorly understood. This review synthesizes current knowledge on the hormonal, transcriptional, and environmental regulation of storage-root enlargement in medicinal plants and highlights future research directions to improve root yield, medicinal quality, and bioactive compound accumulation.