Physiological and Ascorbate -Glutathione pathway-related genes responses under drought and heat stress in crested wheatgrass

Drought and heat stress are two factors that limit the growth of cool-season plant species in many regions of the world. The objective of this experiment was to study the expression patterns of genes involved in ascorbate and glutathione pathways, while assessing the physiological responses of plants and their tolerance to drought stress and heat stress. The results of this study indicated that there were variations in the plants' tolerance to drought and heat among the crested wheatgrass genotypes. Based on the real time-PCR results genes involved in the biosynthesis (GaILDH and gamma-ECS) and recycling (APX, GR, DHAR, MDHAR) of ascorbate and glutathione, also DREB2 were significantly affected by stress. The expression of the DREB2 gene increased substantially in all genotypes under drought and heat stress, which was also associated with high levels of expression genes involved in the Asc-Glu pathway. Based on our results, it seems that all of the genes involved in the Asc-Glu pathway probably had the DRE/CRT element in their promoter region for the DREB2 gene. Sequencing the DREB2 gene showed that leaky mutations occurred in two genotypes collected from cold and wet regions. As a result, the DREB2 probably cannot bind with the dehydration-responsive elements (DRE/CRT, as a cis-acting element) and, although the expression of the DREB2 gene was increased, there was no significant change in the level of expression genes involved in the Asc-Glu pathway. Based on physiological analyses, the ranking of the genotypes' tolerance to drought would appear as 'AC3' > 'AC5' > 'AC6' > 'AC1' > 'AC2' > 'AC4' and the ranking of tolerance to heat stress would be 'AC5' > 'AC1' > 'AC6' > 'AC4' > 'AC2' > 'AC3'. Finally, our results indicated that tolerance to drought and heat associated positively with the expression of genes involved in the Asc-Glu pathway and natural habitat of genotypes. It was also found that the DREB2 plays a key role in regulating the expression of genes involved in the Asc-Glu pathway.