Transcriptomic Insights into Paclobutrazol-Induced Modulation of Metabolic and Signaling Pathways During...

Paclobutrazol (PBZ) is a triazole-type plant growth regulator that interferes with gibberellin (GAs) biosynthesis by blocking the oxidation step that converts ent-kaurene into ent-kaurenoic acid; however, the developmental mechanisms linking GAs restriction with storage organ enlargement remain poorly understood. In potato, PBZ induces compact growth while promoting microtubers (MTs) expansion, suggesting that GAs depletion triggers coordinated developmental reprogramming rather than simply suppressing elongation. Here, we evaluated the phenotypic, histological, and transcriptomic responses associated with PBZ-induced MTs development in Solanum tuberosum L. PBZ treatment, which increased MTs size, suppressed stolon growth, and enhanced starch accumulation, indicating a shift toward storage tissue development. Transcriptomic analysis identified broad PBZ-responsive changes, including enrichment of pathways related to metabolism, ribosome function, carbon metabolism, plant hormone signaling, and cell cycle regulation. Network analyses revealed ATH1-associated modules connected with receptor-like kinases, transcriptional regulators, mitotic regulators, replication-licensing factors and condensin components, supporting coordinated regulation among growth control, localized proliferation, asymmetric division, endoreduplication, and chromatin stability. These patterns were further supported by the absence of a detectable gibberellic acid (GA₃) peak in PBZ-treated samples. These findings support a model in which PBZ-responsive signaling is associated with developmental reprogramming toward radial expansion and reinforcement of storage tissue, providing a regulatory mechanism by which growth repression is coupled to microtube enlargement in potato.