Heat is one of the major environmental stressors that negatively affects alfalfa production. Previously, we reported the role of microRNA156 (miR156) in heat tolerance; however, the mechanism and downstream genes involved in this process were not fully studied. To provide further insight, we compared an empty vector control and miR156-overexpressing alfalfa plants (miR156+) after exposing them to heat stress (40 °C) for 24 h. We collected leaf samples for transcriptome analysis to illustrate the miR156-regulated molecular mechanisms underlying the heat stress response. A total of 3579 differentially expressed genes (DEGs) were detected exclusively in miR156+ plants under heat stress using the Medicago sativa genome as a reference. GO and KEGG analysis indicated that these DEGs were mainly involved in "polysaccharide metabolism", "response to chemical", "secondary metabolism", "carbon metabolism", and "cell cycle". Transcription factors predicted in miR156+ plants belonged to the TCP family, MYB, ABA response element-binding factor, WRKY, and heat shock transcription factor. We also identified two new SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) family gene members (SPL8a and SPL12a), putatively regulated by miR156. The present study provided a comprehensive transcriptome profile of alfalfa, identified a number of genes and pathways, and revealed an miR156-regulated network of mechanisms at the gene expression level to modulate heat responses in alfalfa.
Keywords: Medicago sativa; RNA-seq; alfalfa; heat stress; luzerne; stress thermique; transcriptome.