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Pepper belongs to the Solanaceae family, which includes many important vegetable crops such as tomato, potato, and eggplant. Not only widely used as vegetables and spicy ingredients, pepper also has diverse applications in pharmaceutics, natural coloring agents, cosmetics, defense repellents, and as ornamental plants (Kim et al., 2014;Qin et al., 2014). Pepper is among the most widely cultivated and consumed vegetables in the world, with annual production reaching to 38 million tons in 2011 (www.fao. org). Pepper fruits have significant diversity in morphology and color, and they provide good models for fruit developmental biology (Paran and van der Knaap, 2007;Rivera et al., 2016). Like all other crops, pepper plants are often confronted with different pathogens and pests (Pernezny et al., 2003), and diverse abiotic stress conditions, which necessitate basic studies on the mechanisms of pepper plants responding to various stimuli to facilitate breeding efforts for tolerant cultivars.

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Heat stress (HS), caused by extremely high temperatures, is one of the most severe forms of abiotic stress in pepper. In the present study, we studied the transcriptome and metabolome of a heat-tolerant cultivar (17CL30) and a heat-sensitive cultivar (05S180) under HS. Briefly, we identified 5754 and 5756 differentially expressed genes (DEGs) in 17CL30 and 05S180, respectively. Moreover, we also identified 94 and 108 differentially accumulated metabolites (DAMs) in 17CL30 and 05S180, respectively. Interestingly, there were many common HS-responsive genes (approximately 30%) in both pepper cultivars, despite the expression patterns of these HS-responsive genes being different in both cultivars. Notably, the expression changes of the most common HS-responsive genes were typically much more significant in 17CL30, which might explain why 17CL30 was more heat tolerant. Similar results were also obtained from metabolome data, especially amino acids, organic acids, flavonoids, and sugars. The changes in numerous genes and metabolites emphasized the complex response mechanisms involved in HS in pepper. Collectively, our study suggested that the glutathione metabolic pathway played a critical role in pepper response to HS and the higher accumulation ability of related genes and metabolites might be one of the primary reasons contributing to the heat resistance.