**4. Conclusions**

In this study, thirty-eight *OfXTH* genes were identified from the *O. fragrans* genome database. All of the OfXTH proteins were predicted to locate in the cell wall and were divided into four groups. Multiple segment duplication happened in the evolution of the *OfXTH* genes and contributed to the expansion of *OfXTH* gene family. The expression profiles showed that most *OfXTHs* are closely associated with the flower-opening processes in *O. fragrans*. Using transcriptome and qRT-PCR analysis, five *OfXTH* genes (*OfXTH24*, *27*, *32*, *35* and *36*) were identified and significantly upregulated at the S1 and S2 stages under 19 ◦C treatment, indicating that these *OfXTH* genes might be key regulators responding to ambient temperature to modulate petal cell expansion during flower opening. In conclusion, the present research increased our knowledge of the role of the XTH gene family in floweropening processes in *O. fragrans*.
