Physiological and transcriptional analysis provides insights into responses of a spring wheat variety to combination of salt and heat stresses

Enhancing the frequency and intensity of extreme high temperature conditions due to global warming largely deteriorates salt-induced harm to the crop plants living in saline lands, which leads to losses of agricultural production. In northern China, spring wheat is grown in many slightly saline areas and often subjected to a combination of salt and heat stresses. In this study, a spring wheat cultivar was selected as the experimental material and subjected to salt stress (S), heat stress (H) and their combination (S + H). Physiological analysis showed that the inhibitory effect of S + H stress on wheat growth was much stronger than that of individual salt stress due to aggravating Na⁺ toxicity caused by heat stress. We observed that many genes involved in plant hormones showed much higher expression under S + H stress than under salt stress and heat stress, including key ABA synthesis genes (NCEDs), core ABA signalling transduction genes, key ethylene synthesis genes, and core ethylene signalling transduction genes. Particularly, many ABA-responsive genes (HSFs, HSPs, DHNs and LEAs) were upregulated under S + H stress but not under salt stress and heat stress. DHNs and LEAs were identified to play an important role in preventing cytoplasmic dehydration, protein aggregation, and slowing Na⁺ migration, and ethylene was identified to contribute to Na⁺ detoxification. We propose that in response to S + H stress, wheat plants regulate the expression of DHNs, LEAs, HSPs and HSFs via the ABA pathway to prevent cell dehydration and protein aggregation and keep ion homeostasis via the ethylene pathway.