Histone acetylation and methylation, governed by various histone modification (HM) gene families, are vital for plant biological processes. However, there are limited studies that have explored HMs in ornamental horticultural trees, including sweet osmanthus (Osmanthus fragrans). We performed genome-wide search and identified 208 OfHMs, encompassing 81 histone methyltransferases (OfHMTs), 51 histone demethylases (OfHDMs), 49 histone acetyltransferases (OfHATs) and 27 histone deacetylases (HDACs). Our comprehensive analysis covered chromosome locations, gene structures, conserved domains, cis-acting elements, phylogenetic comparisons, protein interaction networks and functional enrichment pathways for these gene families. Additionally, tandem and fragment replications were unveiled as contributors to the expansion of OfHMs, with some genes exhibiting positive selection. Furthermore, we examined OfHM expression profiles across various tissues and flowering stages, and under 5′-azacytidine (Aza) and ethylene treatments. Most OfHMs displayed heightened expression in leaves, and were downregulated during the flower opening and senescence stages, including OfPRMTs, OfHDTs, OfHDAs, OfSRTs, OfJMJs and OfHAGs; 75.86% and 80.77% of the differentially expressed OfHMs were upregulated after Aza and ethylene treatments, including OfHAGs, OfHDAs and OfSDGs. This study offers a comprehensive analysis of the OfHM gene family, which indicated their potential involvement in ethylene and Aza responses, and in the flowering process. These findings provide valuable insights into the role of OfHMs in flowering and stress responses.

Osmanthus fragrans, a fragrant plant native to China, is extensively utilized in the food and cosmetics industries. However, its optimal harvest period spans only 2–3 days, restricting industrial utilization. Long non-coding RNAs (lncRNAs) have emerged as key regulators of plant growth, yet their roles in O. fragrans petal opening and senescence remain unexplored. Here, we performed high-throughput sequencing of O. fragrans petals across six developmental stages, generating a valuable transcriptomic resource. We identified 57,860 mRNAs and 2414 lncRNAs, including 6499 differentially expressed mRNAs (DEMs) and 494 differentially expressed lncRNAs (DELs). Co-expression and WGCNA analyses revealed key modules associated with petal opening (Turquoise module) and senescence (Blue module). The Blue module, significantly correlated with the S6 senescence stage, contained hub lncRNAs novel_00098659 and novel_00077227 co-expressed with multiple transcription factors and hormone signaling components, including 10 ERFs, OfEIN3, OfJAZ, and OfMYC2. Transient overexpression of novel_00077227 in tobacco accelerated leaf senescence in a hormone-dependent manner, with significant increases in electrolyte leakage and MDA content, and reductions in chlorophyll content and antioxidant enzyme activities. qRT-PCR analysis confirmed that novel_00077227 alters the expression of tobacco homologs of predicted target genes involved in ethylene, auxin, jasmonate, and ABA signaling pathways. This study provides a valuable transcriptomic resource of senescence-associated lncRNAs in O. fragrans and offers evidence for the potential involvement of a key candidate, novel_00077227, in hormone-associated senescence regulation. These findings provide a foundation for future functional studies and potential applications in extending flower longevity.