Transcriptional Insights into Lily Stem Bulblet Formation: Hormonal Regulation, Sugar Metabolism, and Transcriptional Networks in LA Lily ‘Aladdin’

Bulblets, as the main reproductive organ of lilies, have a tremendous impact on the reproductive efficiency of lilies. Cytokinin is known to promote the formation of lily bulblets, but little is known about the mechanisms involved. In this study, a combination of full-length transcriptome and high-throughput RNA sequencing (RNA-Seq) was performed at the leaf axils of LA lily ‘Aladdin’ to characterize the transcriptional response to 6-BA treatment during the critical period of stem-to-bulblet transition. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that 6-BA treatment caused significant changes in starch and sucrose metabolism and plant hormone balance. In particular, the high expression of SUS1 and TPS6 in the 6-BA-treated group suggests that sucrose may act as a key signal to promote bulblet initiation. Furthermore, the induction of elevated expression of genes associated with cytokinin and auxin transport and signaling is crucial for initiating bulblet emergence and stimulating growth. WGCNA analysis revealed that hub TFs such as BLHs, ARFs, HD-ZIPs, AP2/ERFs, and SBPs were significantly overexpressed with genes involved in carbohydrate metabolism and phytohormone signaling, which warranted more in-depth functional studies. This study enriches the understanding of plant hormone-related genes, sugar metabolism-related genes and various transcription factors in the regulation of plant organ development, and lays the foundation for further studies on the molecular mechanisms of lily stem bulblet formation.