Zeatin Regulates Somatic Embryogenesis in Liriodendron sino-americanum via CYCD3

Somatic embryogenesis (SE) is a crucial strategy for in vitro regeneration in woody plants, yet its efficiency is affected by multiple factors, and the underlying regulatory mechanisms remain insufficiently understood. In this study, callus tissues from two Liriodendron sino-americanum genotypes involving different hybrid combinations, ON-LoS and TN-LoS, were treated with varying concentrations (0, 0.005, 0.01, 0.05 mg/L) of exogenous zeatin (ZT) to evaluate its regulatory effect on SE. Treatment with 0.01 mg/L ZT significantly promoted SE in ON-LoS but suppressed it in TN-LoS, indicating that ZT elicited divergent regulatory effects on SE between the two genotypes. To explore the molecular basis of this divergence, transcriptome analysis was conducted at the early stage of SE. Differentially expressed genes (DEGs) were significantly enriched in hormone signaling, particularly in the cytokinin (CK) and brassinosteroid (BR) signaling pathways, as well as biosynthetic and redox-related pathways. In particular, given the established role of cell cycle-related gene CYCD3 (Lchi20922) in promoting cell division, CYCD3 was markedly upregulated by ZT in ON-LoS but downregulated in TN-LoS. These results indicate that ZT regulates SE efficiency through differential modulation of CYCD3 expression in distinct genotypes. This study enhances our understanding of the molecular basis of SE regulation in Liriodendron sino-americanum and offers a theoretical framework for improving regeneration efficiency in woody plants.