Osmanthus fragrans Lour. is popular in landscaping and gardening in Asia. In recent years, growing attention has been given to evergreen tree flowering and adaptation. EARLY FLOWERING3 (ELF3) plays an essential role in plant flowering regulation and abiotic stress tolerance. However, there is very little known about how the ELF3 gene affects flowering time and salt tolerance in O. fragrans. To elucidate the potential role of the flowering-related gene ELF3 in responding to salt tolerance, a significantly upregulated gene OfELF3 was obtained by RNA sequencing (RNA-seq) after salt treatment in O. fragrans. Our results showed that OfELF3 is a nuclear protein, which did not have a transcriptional activation ability. OfELF3 accumulation was determined in different tissues and the differentiation process of floral buds by qRT–PCR, and the gene was also significantly induced by salt stress treatment. In addition, overexpression of OfELF3 accelerated the flowering time of transgenic Arabidopsis lines, and an increase in the expression of flowering integrators such as AtFT, AtSOC1, and AtAP1 was investigated. Moreover, OfELF3 overexpression significantly improved the salt tolerance of transgenic plants, seed germination and root length of transgenic plants and was superior to those of the wild type (WT) under NaCl treatment at 4 days post-germination and the 5-day-old seedling stage, respectively. Similarly, phenotype and physiological indexes (REL, MDA and soluble protein) of 3-week-old transgenic plants were superior to the WT plants as well. Together, our results suggest that OfELF3 is not only a positive regulator in the regulation of flowering but is also involved in the salt tolerance response in O. fragrans.

CCCH is a zinc finger family with a typical CCCH-type motif which performs a variety of roles in plant growth and development and responses to environmental stressors. However, the information about this family has not been reported for Osmanthus fragrans. In this study, a total of 66 CCCH predicted genes were identified from the O. fragrans genome, the majority of which had multiple CCCH motifs. The 66 OfCCCHs were found to be unevenly distributed on 21 chromosomes and were clustered into nine groups based on their phylogenetic analysis. In each group, the gene structure and domain makeup were comparatively conserved. The expression profiles of the OfCCCH genes were examined in various tissues, the flower-opening processes, and under various abiotic stresses using transcriptome sequencing and qRT-PCR (quantitative real-time PCR). The results demonstrated the widespread expression of OfCCCHs in various tissues, the differential expression of 22 OfCCCHs during flower-opening stages, and the identification of 4, 5, and 13 OfCCCHs after ABA, salt, and drought stress treatment, respectively. Furthermore, characterization of the representative OfCCCHs (OfCCCH8, 23, 27, and 36) revealed that they were all localized in the nucleus and that the majority of them had transcriptional activation in the yeast system. Our research offers the first thorough examination of the OfCCCH family and lays the groundwork for future investigations regarding the functions of CCCH genes in O. fragrans.