Transcriptome Profiling and TCP Family Analysis of Broomcorn Millet (Panicum miliaceum L.) Seedlings Under Hyperosmotic Stress

Broomcorn millet (Panicum miliaceum L.) is an early domesticated C-4 cereal crop with high water utilization ability, nutrient content, favored agronomic traits, and tolerance to a broad spectrum of abiotic stresses. Hyperosmotic stress is an inevitable consequence of strong drought on plant, which causes severe dehydration and adversely affects the growth and yield of plants. In this study, we used PEG-6000 to simulate drought conditions and identified differentially expressed gene in broomcorn millet root and shoot under different PEG-6000 concentrations. A total of 11,452 and 14,952 significantly different expression genes (DEGs) were detected separately in root and shoot under at least one PEG treatment. Of these, 2991 and 2051 DEGs were commonly detected at all different PEG levels in root and shoot, respectively, and 535 DEGs were shared in both root and shoot at all different PEG levels, including six genes differently regulated in root and shoot. Enrichment analysis categorized these DEGs into 85 and 56 GO terms, or 17 and 6 significant KEGG pathways in root and shoot, respectively. And 39 hub genes especially longmi029229 associated with hyperosmotic stress were detected by weighted gene co-expression network analysis. In addition, 29 TCP transcription factors were identified and characterized in broomcorn millet, which were divided into three clades. Phylogenetic analysis indicated that the TCPs of monocot broomcorn millet and rice were closer than the TCPs of monocot broomcorn millet and dicot Arabidopsis. Analysis of the expression pattern of PmTCPs to drought stress indicated that 11 and 20 TCP genes showed significant change under PEG-6000 treatment in root and shoot separately. These DEGs and PmTCP genes with differential expression patterns in shoot and root deserve further study for uncovering the mechanism of drought resistance in broomcorn millet.