**5. Conclusions**

In this study, 25 *SWEET* genes were firstly identified and analyzed in *R. chinensis* 'Old Blush'. Gene structure and motif analysis indicated that members of the SWEET family in the rose are highly conserved among the species. The prediction of *Cis*-acting elements suggested that some family members may be involved in complex signaling pathway regulation. The transcriptome data showed that there were at least eight DEGs of *SWEETs* in the leaves and shoots of *R. chinensis* 'Old Blush' and *R. beggeriana* after cold treatment. The qRT-PCR results further disclosed that there were various expression patterns of *SWEET* genes in two species. *SWEET1* and *SWEET4b* were relatively conserved in *Rosa* L., with similar increased trends both in tissues and species. However, *SWEET2a* and *SWEET10c* exhibited the species difference after cold treatment that sharply upregulated in the leaves of the deciduous and extremely cold-tolerant species *R. beggeriana* but not the evergreen and moderately cold-tolerant species *R. chinensis* 'Old Blush'. The results indicated that *SWEET2a* and *SWEET10c* might be the crucial candidates to participate in the acquisition of cold tolerance in rose. Our findings provide important information for further research on the function analysis of *SWEET* genes in cold response and their application in the breeding of rose varieties with strong cold tolerance.

**Supplementary Materials:** The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/plants12071474/s1, Figure S1: The transmembrane structure of 25 RcSWEET proteins; Table S1: Primers used in this study; Table S2: Nucleotide sequences of 25 *RcSWEET* genes; Table S3: Amino acid sequences of 63 SWEET proteins from three species; Table S4: Estimated Ka/Ks ratios of the duplicated RcSWEET genes; Table S5: The numbers of predicted cis-elements in the promoters of 25 *RcSWEET* genes; Table S6: Transcriptome sequencing data of *RcSWEET* genes in different tissues (PRJNA546486); Table S7: Transcriptome sequencing data of *RbSWEET* genes in leaves and shoots during cold treatment.

**Author Contributions:** Conceptualization, H.G. and S.Y.; methodology, X.S., Y.K., M.D. and X.Y.; software and validation, X.S., B.F. and R.J.; investigation, S.Y., X.S., M.D. and X.Z.; formal analysis, X.S., Y.K. and S.Y.; resources, S.Y.; data curation, X.S. and S.Y.; writing—original draft preparation, X.S.; writing—review and editing, Y.K. and S.Y.; visualization, X.S., R.J. and X.Z.; supervision, H.G. and S.Y. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study was supported by the National Key R&D Program of China (2018YFD1000401; 2019YFD1000401) and the Beijing Innovation Consortium of Agriculture Research System, China (BAIC09-2023).

**Data Availability Statement:** All data are included in the main text.

**Conflicts of Interest:** The authors declare no conflict of interest.
