Exogenous EBR enhanced heat tolerance in mini Chinese cabbage by regulating ABA accumulation

• EBR pretreatment can reduce reactive oxygen species (ROS) under heat stress, protect the photosynthetic system, and maintain stomatal function. • We speculated that EBR and ABA may have a synergistic effect to jointly promote the heat resistance of mini Chinese cabbage. • EBR pretreatment significantly increased the relative expression levels of BrNCED3 and BrPYL genes, and decreased the relative expression levels of BrCYP707A1 genes. • Exogenous EBR can improve the heat resistance of mini Chinese cabbage by regulating ABA accumulation. It is unclear whether 24-epibrassinolide (EBR) can improve the heat resistance of mini Chinese cabbage ( Brassica pekinensis ). Whether abscisic acid (ABA) can be involved in EBR to improve the heat tolerance of mini Chinese cabbage is not clear. Therefore, in this study, mini Chinese cabbage was used as experimental material, and the effects of EBR/ABA and its synthetic inhibitors were studied by applying pharmacological methods to explore the effects of EBR and ABA on improving the heat resistance of mini Chinese cabbage. Our experimental results revealed that EBR pretreatment can reduce reactive oxygen species (ROS) under heat stress, protect the photosynthetic system, and maintain stomatal function, improving the heat resistance of mini Chinese cabbage. It is noteworthy that the application of fluriddone (FDT) or brassinazole (Brz) to EBR or ABA treated mini Chinese cabbage significantly reduced the stability of the membrane system and photosynthetic system. Based on these observations, we speculated that EBR and ABA may have a synergistic effect to jointly promote the heat resistance of mini Chinese cabbage. Transcriptome result showed that EBR pretreatment significantly increased the relative expression levels of BrNCED3 and BrPYL genes, and decreased the relative expression levels of BrCYP707A1 genes. These results suggested that EBR activates downstream signaling pathways by promoting ABA accumulation under heat stress. In conclusion, exogenous EBR can improve the heat resistance of mini Chinese cabbage by regulating ABA accumulation. This study provides new insights into the potential mechanism of EBR alleviating heat stress in mini Chinese cabbage. Under high temperature stress, exogenous EBR can promote the accumulation of endogenous ABA by up-regulating the expression of ABA synthesis gene BrNCED3 and down-regulating the expression of ABA metabolism gene BrCYP707A1 , so as to activate ABA downstream signal transduction factor BrPYL , enhance photosynthesis and protective membrane system to start heat resistance pathway and improve the heat tolerance of mini Chinese cabbage. The solid lines denote the established pathways, whereas the dashed lines signify pathways that are yet to be determined. Arrowheads symbolize a promoting effect, and the short horizontal lines indicate an inhibiting effect.