**5. Conclusions**

*helicase-15* and *UBC28* can be used as internal reference genes when detecting gene expression pattern in different tissues of *L. megaphylla*. *ACT7* and *UBC36* were considered to be the most suitable internal reference genes at different leaf developmental stages of *L. megaphylla*. *UBC36*, *TCTP*, *PAB2,* and *CYP20* were optimum reference genes when *L. megaphylla* was suffering from abiotic stress. Among them, *UBC36* and *TCTP* were the best under cold treatment, while *PAB2* and *CYP20-2* were the best under heat treatment. We recommend that two internal reference genes be used to normalize RT-qPCR data in future experiments. In short, our results lay a foundation for future molecular biology research on *L. megaphylla*.

**Supplementary Materials:** The following supporting information can be downloaded at: https:// www.mdpi.com/article/10.3390/plants12112185/s1, Figure S1: The PCR products electrophoresis result of the 20 candidate reference genes; Figure S2: Melting curves of the 20 candidate reference genes in *L. megaphylla*. Table S1: The cDNA sequences of the 20 candidate reference genes from *L. megaphylla*; Table S2: Primer sequences of candidate reference genes in *L. megaphylla*.

**Author Contributions:** H.L. and Y.L. conceived and designed the research; H.L., J.L. (Jing Liu), P.C., X.Z. and K.W. conducted the experiments; H.L. drafted the manuscript; Y.L., P.C. and J.L. (Jiuxing Lu) revised the manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** The research was supported by the National Natural Science Foundation of China (no. 32201615), the Science and Technology Invigorating Forestry Foundation of He'nan Province (no. YLK202211), and the Key Technology R&D Program of He'nan Province (No. 232102111106).

**Data Availability Statement:** All data needed to evaluate the conclusions in this paper are present in the paper and/or the Supplementary Materials.

**Acknowledgments:** We thank the anonymous reviewers for their comments. The authors specifically thank Anita K. Snyder for language editing; their efforts greatly improved the manuscript. We also thank Ruimin Li for revising the manuscript.

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