Simple Summary
High-temperature stress limits the yield and quality of pepper (Capsicum annuum L.), especially under protected cultivation. We performed physiological and transcriptome analyses on two pepper lines with divergent heat tolerance. The tolerant line kept its chlorophyll and antioxidant defenses active with little membrane damage, whereas the sensitive line responded briefly and suffered increasing damage. GO and KEGG enrichment analyses uncovered conserved core heat-responsive pathways exhibiting genotype-dependent transcriptional dynamics. Small heat-shock protein (HSP20) genes were strongly induced and confirmed by qRT-PCR. This study characterizes pepper seedlings’ transcriptional responses to heat and provides candidate genes for breeding heat-tolerant peppers.
Abstract
Global climate change and warming are increasing challenges to plant growth, development, and crop productivity. To investigate the responses of pepper seedlings to short-term high-temperature stress, we performed time-course physiological and transcriptome analyses on leaves of a heat-tolerant line (J18-1) and a heat-sensitive line (J190) at the 6–8 true leaves stage after exposure to 42 °C for 0, 6, and 24 h. Comparisons were made within each line using 0 h as the baseline. Under high-temperature stress, J18-1 maintained chlorophyll without degradation, with SOD, POD, and CAT activities increasing at 6 h and remaining elevated at 24 h, and MDA content remaining low. In contrast, J190 showed a transient chlorophyll increase that returned to the baseline at 24 h, with antioxidant enzyme activities increasing at 6 h but declining at 24 h, and MDA content increasing at 6 h and remaining elevated at 24 h. In total, 16,912 differentially expressed genes (DEGs) were identified across all comparisons. GO and KEGG enrichment analyses indicated that protein processing in the endoplasmic reticulum and plant hormone signal transduction were the most significantly enriched pathways, in which HSP20 and ERF genes showed genotype-dependent expression changes. qRT-PCR confirmed that HSP20 genes were up-regulated at both 6 h and 24 h under high-temperature stress, consistent with the transcriptome data. These results provide candidate genes and pathways for elucidating pepper seedling responses to short-term high-temperature stress.