Kentucky bluegrass (Poa pratenesis) is one of the most widely used cool-season turfgrass，but it is sensitive to drought stress. Molecular studies in Kentucky bluegrass are hindered by its large and complex genome structure. In this study, a comparative transcriptomic study between a short and long period of water deficiency was conducted. Three transcriptome libraries were constructed and sequenced with PEG6000-treated plants at 0 h, 2 h, and 16 h after drought stress. A total of 199,083 differentially expressed genes (DEGs) were obtained. The DEGs were identified from three pairwise comparisons: 15,536 up-regulated and 14,770 down-regulated in 2 h vs 0 h; 16,420 up-regulated and 14,498 down-regulated in 16 h vs 2 h; and 5,110 up-regulated and 4,030 down-regulated in 16 h vs 0 h. Among which, 24 up-regulated and 36 down-regulated DEGs were continuously expressed during the entire drought period. Gene ontology (GO) analysis demonstrated that the DEGs were mainly clustered in ‘Catalytic activity’, ‘Binding’ and ‘Transporter activity’ in the molecular function category,‘Cellular process’, ‘Metabolic process’ and ‘Single-organism process’ in the biological process category, ‘cell’, ‘cell part’ and ‘organelle’ in cellular components category. The Kyoto Encyclopedia of Genes and Genomes (KEGG) annotation revealed that DEGs were enriched in ‘Plant hormone signal transduction’, ‘MAPK signaling pathway-Plant’, ‘FoxO signaling pathway’, ‘mTOR signaling pathway’, ‘Sesquiterpenoid and triterpenoid biosynthesis’ and ‘Arginine and proline metabolism’. Some key up-regulated genes, including PP2C, ABF, PYL, BSK, TCH4, COI1, JAZ, and MYC2, were involved in hormone signaling transduction of abscisic acid, jasmonic acid, and brassinosteroid and may play important roles in coping with drought stress in Kentucky bluegrass. The transcriptome of Kentucky bluegrass in response to drought stress provided substantial molecular information for further genomic analysis of turfgrasses. Our findings indicate that some key genes involved in endogenous hormone signal transduction could be ideal targets for drought tolerance improvement in turfgrass breeding.
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