Comparative physiological and transcriptomic analysis of sesame cultivars with different tolerance responses to heat stress

High temperature is the main factor affecting plant growth and can cause plant growth inhibition and yield reduction. Here, seedlings of two contrasting sesame varieties, i.e., Zheng Taizhi 3 (heat-tolerant) and SP19 (heat-sensitive), were treated at 43 °C for 10 days. The results showed that the relative electrical conductivity, hydrogen peroxide levels, and superoxide anion radical levels of both varieties increased significantly under high temperature stress. Additionally, dry matter accumulation and chlorophyll content decreased significantly, and the activities of peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD) increased. However, under HT stress, the content of reactive oxygen species in Zheng Taizhi 3 was lower than that in SP19, and the activities of SOD, CAT, and POD as well as the chlorophyll content in Zheng Taizhi 3 were higher than those in SP19. Comparative transcriptome analysis identified 6736 differentially expressed genes (DEGs); 5526 DEGs (2878 up and 2648 down) were identified in Zheng Taizhi 3, and 5186 DEGs (2695 up and 2491 down) were identified in SP19, with 3976 overlapping DEGs. These DEGs included stress tolerance-related heat-shock proteins, as well as genes related to carbohydrate and energy metabolism, signal transduction, endoplasmic reticulum protein processing, amino acid metabolism, and secondary metabolism. Overall, our results showed that the heat tolerance of Zheng Taizhi 3 was attributed to a stronger antioxidant defense system, enabling the variety to avoid oxidative damage compared with the heat-sensitive SP19. Moreover, some specifically expressed and high-abundance genes in Zheng Taizhi 3 were involved in regulatory mechanisms related to heat tolerance, including plant hormone signal transduction and heat shock protein regulation, thereby enhancing heat tolerance. The study contributes to a deeper understanding of the underlying complex molecular mechanisms involved in the responses of sesame seedlings to heat stress and provides a potential strategy for heat-resistant new varieties.