Transcriptomics and Plant Hormone Analysis Reveal the Mechanism of Exogenous GA3 Promoting Reflowering of Phalaenopsis ‘Hatuyuki’

<i>Phalaenopsis</i> orchids are globally significant high-value ornamental flowers due to their strange flower shape, gorgeous color, and long flowering period. The successful implementation of reflowering technology is expected to double the economic value of the <i>Phalaenopsis</i> industry. This study selected the cultivated variety <i>Phalaenopsis</i> 'Hatuyuki' as the material to investigate the effects of exogenous gibberellin A₃ (GA₃) application (0, 50, 100, 150, and 200 mg/L) on its reflowering. Growth phenotype analysis indicates that exogenous GA₃ significantly promotes the occurrence of reflowering in <i>Phalaenopsis</i> 'Hatuyuki' after the first flowering, specifically manifested in elongated leaves, flower bud differentiation, flower stalk growth, and an earlier onset of flowering. The application of exogenous GA₃ significantly enhances the accumulation of starch, soluble sugars, and proteins in <i>Phalaenopsis</i> 'Hatuyuki', while inhibiting the synthesis of free fatty acids. Gibberellins (GA₃, gibberellin A₁ (GA₁), and gibberellin A₈ (GA₈)), cytokinins (6-Benzyladenosine (BAPR) and Kinetin (K)), and indole-3-acetic acids (IAAs) (tryptamine (TRA), indole-3-acetic acid (IAA)) are the core endogenous hormones responding to exogenous GA₃ spraying treatment. Transcriptome analysis identified a total of 3891 differentially expressed genes (DEGs). The KEGG enrichment analysis revealed that the most significantly enriched KEGG pathways included 'Plant hormone signal transduction'. Key genes involved in the plant hormone signal transduction pathway (<i>AUX</i>, <i>IAA</i>, <i>SAUR</i>, <i>DELLA</i>, <i>MYC2</i>) were validated through qRT-PCR, suggesting that these genes may be crucial for the exogenous GA₃ application that promotes the reflowering of <i>Phalaenopsis</i> 'Hatuyuki'. Additionally, this study highlights 202 core DEGs responsive to exogenous GA₃. Combined with the analysis of hormone signaling pathways, it provides a new perspective for uncovering the key molecular modules involved in GA₃-regulated reflowering of <i>Phalaenopsis</i> 'Hatuyuki'. Overall, the findings of this study indicate that exogenous GA₃ application can promote the re-flowering of <i>Phalaenopsis</i> 'Hatuyuki'.