*Article* **CaHSP18.1a, a Small Heat Shock Protein from Pepper (***Capsicum annuum* **L.), Positively Responds to Heat, Drought, and Salt Tolerance**

**Yan-Li Liu 1,†, Shuai Liu 1,†, Jing-Jing Xiao 1, Guo-Xin Cheng 1, Haq Saeed ul 1,2 and Zhen-Hui Gong 1,\***


**Abstract:** Pepper is a thermophilic crop, shallow-rooted plant that is often severely affected by abiotic stresses such as heat, salt, and drought. The growth and development of pepper is seriously affected by adverse stresses, resulting in decreases in the yield and quality of pepper crops. Small heat shock proteins (s HSPs) play a crucial role in protecting plant cells against various stresses. A previous study in our laboratory showed that the expression level of *CaHSP18.1a* was highly induced by heat stress, but the function and mechanism of CaHSP18.1a responding to abiotic stresses is not clear. In this study, we first analyzed the expression of *CaHSP18.1a* in the thermo-sensitive B6 line and thermo-tolerant R9 line and demonstrated that the transcription of *CaHSP18.1a* was strongly induced by heat stress, salt, and drought stress in both R9 and B6, and that the response is more intense and earlier in the R9 line. In the R9 line, the silencing of *CaHSP18.1a* decreased resistance to heat, drought, and salt stresses. The silencing of *CaHSP18.1a* resulted in significant increases in relative electrolyte leakage (REL) and malonaldehyde (MDA) contents, while total chlorophyll content decreased under heat, salt, and drought stresses. Overexpression analyses of *CaHSP18.1a* in transgenic *Arabidopsis* further confirmed that *CaHSP18.1a* functions positively in resistance to heat, drought, and salt stresses. The transgenic *Arabidopsis* had higherchlorophyll content and activities of superoxide dismutase, catalase, and ascorbate peroxidase than the wild type (WT). However, the relative conductivity and MDA content were decreased in transgenic Arabidopsis compared to the wild type (WT). We further showed that the CaHSP18.1a protein is localized to the cell membrane. These results indicate CaHSP18.1a may act as a positive regulator of responses to abiotic stresses.

**Keywords:** *CaHSP18.1a*; gene silencing; transgenic *Arabidopsis*; heat stress; pepper; gene expression
