Overexpression of barley heat stress transcription factor HvHsfA6a provides thermotolerance by modulating transcriptome and metabolome

Global climate change has adverse impacts on crop production. Plants have an innate mechanism to combat the ill effects of temperature alterations. Heat shock factors (HSFs) are crucial transcription factors involved in developmental processes and various heat stress-associated rescue mechanisms. Here, we functionally characterize a highly heat stress-responsive HvHsfA6a in barley by developing constitutively overexpressing transgenic lines. The transgenic lines show a heat-tolerant phenotype via improved photosynthesis, antioxidants, and upregulation of HSPs and metabolites involved in stress amelioration. Global transcriptomics and ChIP sequencing revealed that HvHsfA6a orchestrates the expression of several genes through direct binding with other HSFs containing consensus HSE in their promoter regions. A GC-MS-based metabolomics analysis also revealed alterations in key metabolic processes such as carbohydrate metabolism, citric acid cycle, amino acids, and secondary metabolism. Higher accumulation of key metabolites such as sucrose, galactinol, shikimate, and ascorbate has been observed under both control and heat stress in transgenic lines as compared with wild-type plants. Moreover, higher jasmonic acid accumulation in transgenic lines also aids in enhancing thermotolerance. Overall, the results suggest that overexpression of HvHsfA6a primes the plants for heat stress conditions by alteration in gene expression and metabolic status.