Discovery, expression profiling, and evolutionary analysis of Cynodon expressed sequence tags
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Bermudagrass (Cynodon dactylon) is a major turfgrass species for sports fields, lawns, parks, golf courses, and general utility turfs in tropical and subtropical regions. Despite its ecological importance, much of its study has been dependent upon classical approaches. Information about Bermudagrass at the molecular level has been deficient although molecular information for other plants has been accumulated for the last two dacades. In the current study, we constructed a normalized cDNA library from leaf tissue of Bermudagrass in order to expand our knowledge of its transcriptome. We sequenced and annotated 15,588 expressed sequence tags (ESTs), which were deposited in the National Center for Biotechnology Information (NCBI) to be shared with other scientists. We also conducted cDNA array hybridization (macroarray) to profile genes responding to drought stress. A total of 120 and 69 genes were identified as up- and down-regulated, respectively. BLASTX annotation suggested that up-regulated genes may be involved in osmotic adjustment, signal transduction pathways, protein repair systems, and removal of toxins, while down-regulated genes were mostly related to basic plant metabolism such as photosynthesis and glycolysis. Using the cDNA sequences, we performed a comparative genomic study to gain new insight into the evolution of Bermudagrass. Results suggested that the common ancestor of the grass family experienced a whole genome duplication event at ca. 50.0 ~ 65.4 million years ago (MYA), before the divergence of the PACC and BEP clades at ca. 42.3 ~ 50.0 MYA. This evolutionary study also provided concrete evidence that the Chloridoideae and Panicoideae subfamilies diverged from a common ancestor at ca. 34.6 ~ 38.5 MYA. However, we were not able to find any evidence of a recent whole genome duplication event in Bermudagrass, possibly due to its autopolyploid genome structure.