Comparative transcriptomic analysis reveals gene expression in response to cold stress in Rhododendron aureum Georgi

One of the important factors restricting plant growth and their regional distribution is cold stress. To acclimatize to cold conditions, plants growing in temperate zones reprogram their gene expression to better cope with cold stress. However, the climate is complex and tends to change. For example, a sudden large decrease in the temperature drop can seriously affect plants. Rhododendron aureum Georgi, an evergreen plant growing in high-altitude areas of Changbai Mountain, exhibits different cold tolerance characteristics in response to the harsh ecological environment. In our study, we constructed six cDNA libraries by extracting and enriching the mRNA of seedlings grown under normal temperature and cold stress. Furthermore, 103,951 and 102,370 unigenes were generated through de novo assembly, out of which 12,261 genes were identified as differentially expressed genes related to cold stress, including 5450 up-regulated and 6811 down-regulated genes. Genes involved in calcium and hormone signal transduction, cell homeostasis restoration, and lipid metabolism were up-regulated after Rhododendron plants were exposed to cold stress, whereas several transcripts encoding photosystem reaction center subunits and multidrug and toxic compound extrusion proteins were down-regulated. In addition, transcription factors related to abiotic stress, HSFA1 and NPR1 encoding genes were up-regulated after cold stress; however, CBF transcripts did not show significant differential expression. Five genes of interest were selected for verification by quantitative real-time polymerase chain reaction (PCR). Although the relative expression of all five genes obtained by quantitative (q)RT-PCR was not completely in line with RNA-sequencing (RNA-seq), the changing trends of the data obtained by the two methods were consistent. Our results provide a transcriptome profile of Rhododendron's response to cold stress. These data will provide insights for elucidating the molecular mechanisms of cold tolerance in alpine plants.