**2. Materials and Methods**

## *2.1. Plant Materials and Growth Conditions*

The thermo-tolerant pepper line R9 (a sweet pepper from the World/Asia Vegetable Research and Development Center, PP0042-51) and the thermo-sensitive pepper line B6 (selected by the Pepper Research Group, College of Horticulture, Northwest A&F University, Yangling, China) were used in this study. Pepper seedlings were cultivated in a growth chamber under the following growth conditions prior to various treatments: daily 16 h light/8 h dark cycles and 65% relative humidity until the 6–8 true leaves stage. The temperature was changed throughout the course of the experiment. R9 peppers were grown under 25/20 ◦C day/night temperatures to enable analyzing gene expression [30,36,37]. However, the growing conditions for use of virus-induced gene silencing (VIGS) in the R9 pepper line were 22/18 ◦C day/night temperatures [38]. *Arabidopsis* ecotype Col-0 variety seedlings were incubated at 65% relative humidity, 22/18 ◦C (day/night), and 16 h/8 h (light/dark) photoperiod conditions [37,38].
