Heat stress-responsive miRNA are transiently expressed to impart stress tolerance in wheat plants

With rising global temperature, understanding plants adaptation to heat stress has implication in plant breeding. The prominent role of miRNA-guided gene expression has been uncovered in several stress responses. In this study, leaf tissues were harvested from four biological replicates of control and heat stressed wheat plants at 0, 1 and 4 days after treatment (DAT). A total of 24 small RNA libraries were sequenced on the Illumina platform, generating 55 million reads corresponding 18 million distinct tags. These tags were mapped to previously annotated miRNA precursors and a total of 208 miRNAs were identified. Forty-seven of these were differentially expressed in response to heat stress. Approximately 63% of the differentially expressed miRNAs were transiently downregulated immediately following the heat stress but their expression levels were similar to control plants four days later. MiRNA downregulated in response to heat stress included miR159, miR169, miR171, miR528 and miR1122 which were predicted to target transcription factors, signal transduction pathways and antioxidant activity. MiR1122 and miR171 were also predicted to target methyl transferases and dicer-like 3, respectively. To verify miRNA-guided cleavage sites, the corresponding 24 degradome libraries were sequenced and approximately 370 million reads were mapped and analyzed using the CleaveLand pipeline. Cleaved targets of miR159, miR169 and miR1122 corresponding to transcripts involved in DNA binding and protein kinase activity were identified in the degradome libraries. Accurate identification and validation of miRNA and their target is essential to develop novel regulatory gene based wheat breeding strategies.