Transcriptome Analysis of the Cytokinin Response in Medicago truncatula

As an important legume plant, Medicago truncatula is a preeminent model for the study of the processes of nitrogen fixation, symbiosis, and legume genomics. The regulatory mechanism of the cytokinin response has been studied in many plants, such as rice, Arabidopsis, tomato, and barley, but information about regulatory pathways and genes involved in the cytokinin response in Medicago truncatula is notably limited. In this study, to better understand the cytokinin response in Medicago truncatula, transcriptome analysis of seedlings grown with 6-benzylaminopurine or lovastatin was performed using RNA-Seq. In this study, 3627 and 3093 transcripts were differentially expressed in cytokinin-induced/control (Cyto/Ctrl) and cytokinin-inhibited/control (Inh/Ctrl) groups, respectively, and differentially expressed genes were tested by quantitative real-time PCR (qRT-PCR). Analysis of the cytokinin response in Medicago truncatula revealed a large number of transcripts involved in signal transduction, metabolic process, secondary metabolite biosynthesis, transport and catabolism, growth and development, defense mechanisms, and transcription. There were 43 transcription factor families, including 1845 transcription factor (TF) genes with 2147 TF transcripts, as detected by RNA-Seq. Additionally, 216 TF genes with 220 transcripts were differentially expressed in Cyto/Ctrl, and 185 TF genes with 189 transcripts were in Inh/Ctrl. A total of 289 and 260 DETs involved in biosynthesis, metabolism, and transduction of plant hormones were identified in the Cyto/Ctrl and Inh/Ctrl groups, respectively. Furthermore, 15 transcripts, including A-ARR, IPT, and CKX, were demonstrated to play roles in cytokinin regulation or signal transduction. These findings were associated with the cytokinin response in other plants. The resulting data provide the first cytokinin transcriptome analysis in Medicago truncatula. Further analysis and identification of cytokinin-regulated transcripts or signal transduction transcripts may help to elucidate the regulatory mechanisms governing the cytokinin response in Medicago truncatula.