In China, Prunus mume is a famous flowering tree that has been cultivated for 3000 years. P. mume grows in tropical and subtropical regions, and most varieties lack cold resistance; thus, it is necessary to study the low-temperature response mechanism of P. mume to expand the scope of its cultivation. We used the integrated transcriptomic and metabolomic analysis of a cold-resistant variety of P. mume ‘Meiren’, to identify key genes and metabolites associated with low temperatures during flowering. The ‘Meiren’ cultivar responded in a timely manner to temperature by way of a low-temperature signal transduction pathway. After experiencing low temperatures, the petals fade and wilt, resulting in low ornamental value. At the same time, in the cold response pathway, the activities of related transcription factors up- or downregulate genes and metabolites related to low temperature-induced proteins, osmotic regulators, protective enzyme systems, and biosynthesis and metabolism of sugars and acids. Our findings promote research on the adaptation of P. mume to low temperatures during wintering and early flowering for domestication and breeding.

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.