Alfalfa transcriptome profiling provides insight into miR156-mediated molecular mechanisms of heat stress tolerance.

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, mechanisms 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 24h. We collected leaf samples for transcriptome analysis to illustrate the miR156-regualted molecular mechanisms underlying the heat stress response. A total of 3579 differentially expressed genes (DEG) were detected exclusively in miR156+ plants under heat stress using the Medicago sativa genome as 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 TCP family, MYB, ABA response element-binding factor, WRKY and heat shock transcription factor. We also identified two new SPL family gene member (SPL8a and SPL12a), putatively regulated by miR156. The present study provides comprehensive transcriptome profile of alfalfa, identifies a number of genes and pathways, and reveals a miR156-regulated network of mechanisms at the gene expression level to modulate heat responses in alfalfa.