Genome-Wide Analysis of the EIN3/EIL Transcription Factors in Osmanthus fragrans and Their Stress Response to Azacytidine (AZA) and Ethylene (ETH) Treatment

Ethylene-insensitive 3/ethylene-insensitive 3-like (EIN3/EIL) transcription factors are central regulators of ethylene signaling and stress adaptation in plants. However, their roles in Osmanthus fragrans, a globally cherished ornamental and aromatic plant with significant economic value, remain poorly characterized. Here, we identified nine OfEIL genes across eight chromosomes in the O. fragrans “Liuye Jingui” genome. Conserved motif analysis revealed core domains (Motif1/2/4/7), and promoter cis-elements highlighting hormone-related, stress-related, and growth-related regulatory potential. During late flowering stages, six OfEILs (3/4/5/6/7/9) were significantly upregulated. Under 5-azacytidine (AZA, a DNA demethylation agent), OfEIL2 and OfEIL7 were downregulated, whereas the ETH treatment activated OfEIL3/7/8/9. Strikingly, OfEIL7 exhibited dual regulatory roles, correlating strongly with natural flowering progression, AZA-induced demethylation, and ETH responses. Functional divergence was observed in petal senescence, with OfEIL2–5 and OfEIL7–9 showing stage-specific and tissue-specific expression patterns. These results position OfEIL7 as a key hub integrating epigenetic and hormonal signals to modulate floral longevity and stress adaptation. Our study provides the first genome-wide characterization of the EIL family in O. fragrans, offering critical insights for molecular breeding aimed at enhancing ornamental traits and environmental resilience in this economically significant species.