Transcriptomic Profiling Revealed Genes Involved in Response to Drought Stress in Alfalfa

Drought stress is a primary abiotic stress that causes the crop losses worldwide. Under drought conditions, root growth is determined by the action of environmental drought stress through specific genes that adapt root development to water-limited conditions. We observed that root length, root-to-shoot ratio, and ABA content increased under water stress. To precisely identify drought-responsive genes and depict the drought response of alfalfa roots at the transcriptomic level, alfalfa (Medicago sativa L.) was grown in a split-root system in the experiment. Half of the alfalfa root system was watered at field capacity, and the other half of the root system was subjected to drought conditions. Illumina sequencing using RNAs obtained from these two half-root systems was performed to identify the drought-responsive gene expression patterns of alfalfa. In total, 5484 differentially expressed genes (DEGs) were identified and DEGs were significantly enriched in 268 GO terms and 14 KEGG pathways. Gene response to microorganism and associated membrane components were determined to be strongly induced by drought conditions. The major pathways involved in the drought response were involved in plant-pathogen interactions, plant hormone signal transduction, MAPK, and phenylpropanoid biosynthesis pathways. In addition, 392 lncRNAs and 1538 TFs that participated in the alfalfa root response to drought were identified. The major TFs involved in regulating the drought response included NAC, WRKY, bHLH, MYB, and B3. The results of this study may provide a reference for further research investigating drought-responsive gene expression and regulation patterns in the alfalfa roots.