**5. Conclusions**

In this study, we first analyzed the expression of *CaHSP18.1a* in R9 and B6 pepper lines and demonstrated that *CaHSP18.1a* was expressed when induced by abiotic stress factors such as high temperature, drought, and high salinity. *CaHSP18.1a* silencing decreased the resistance of pepper plants to heat, drought, and salt stresses through different molecular and physiological mechanisms. Overexpression analyses of *CaHSP18.1a* in transgenic *Arabidopsis* further confirmed that *CaHSP18.1a* functions positively in responses to heat, drought, and salt stresses. The expression levels of other stress-related genes were also measured, and some were determined to be significantly affected by *CaHSP18.1a* overexpression. We further confirmed that *CaHSP18.1a* protein was localized in the cell membrane. Collectively, these results show *CaHSP18.1a* likely acts as a positive regulator of the response to abiotic stresses in pepper.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/ 10.3390/horticulturae7050117/s1, Figure S1: Detection of silencing efficiency of CaHsp18.1a gene mediated by TRV2; Figure S2: Validation and acquisition of homozygous strain of T3 generation of Arabidopsis with overexpression of CaHsp18.1a; Figure S3: Germination of the transgenic Arabidopsis under salt stress; Table S1: The main primers sequence used in this research.

**Author Contributions:** S.L., Y.-L.L. and Z.-H.G. conceived and designed the research; S.L. and Y.-L.L. conducted the experiments and wrote the manuscript; G.-X.C. and Y.-L.L. analyzed the data; H.S.u., S.L. and J.-J.X. critically revised the manuscript; Z.-H.G. contributed reagents and funded the project. All authors have read and agreed to the published version of the manuscript.

**Funding:** We highly appreciate the financial support of the funding from the National Natural Science Foundation of China (No. U1603102, No. 31772309).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data is contained within the article.

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