**5. Conclusions**

This is the first report of the effects of long-term adaptation to warmer growth conditions or HT-adaptation of the gene expression profile in crops. We were able to derive the following conclusions from this study. Many DEGs were overlapping between minor-warming and warming conditions and in both lines examined, Chiifu and Kenshin. Most HT adaptation-associated genes in Chinese cabbage are homologous to acquired thermotolerance-related genes in *Arabidopsis*. Sixteen putative HT adaptation-related genes were identified: 10 HSR genes (including *BrHSFA2* and *sHSP*s), 2 TF genes

(*BrPIF6* and a *BrMyB*), 1 SF gene (Pre-mRNA splicing Prp18-interacting factor, *BrSMP1*), and 3 other genes. Three additional genes, *BrPIF4*, *BrROF2*, and *BrMPSR1*, were also identified as candidate genes involved in HT adaptation. The degree of expression of *HSR* genes such as *BrHSP18.2*s appears to be related to the levels of HSF protein such as BrHSFA2 rather than their own promoter activity. Adaptation to HT in Chinese cabbage appears to be due to changes in the auxin response, increases in the alternative splicing of *BrHSFA2* to amplify its expression, HS memory of HSR genes, and their increases in expression upon recurring HT. The genes identified in this study could be utilized in molecular breeding and marker development after further analysis.

**Supplementary Materials:** Supplementary materials can be found at http://www.mdpi.com/1422-0067/19/6/ 1727/s1.

**Author Contributions:** Conceptualization: H.Y., C.-T.H., Y.H. Data curation: J.Y.A., X.D., C.-T.H. Formal analysis: J.Y.A., M.S. Funding acquisition: Y.H. Investigation: J.Y.A., X.D. Methodology: H.S., M.S., K.Y. Software: X.D., J.Y.A. Supervision: Y.H. Validation: J.Y.A., X.D., H.Y., Y.H. Writing-original draft: X.D., J.Y.A. Writing-review & editing: H.Y., C.-T.H., Y.H.

**Acknowledgments:** This work was supported by a grant from the Research Fund of Chungnam National University (CNU), Daejeon, Korea, to Yoonkang Hur (2017-1828-01).

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