Transcriptomic analysis reveals crucial biological pathways associated with cold response in Camellia weiningensis in Guizhou Province, China

Abstract

Camellia weiningensis Y.K.Li.sp.nov. is a tea-oil tree species with excellent commercial properties and strong resistance to cold temperatures in Weining County, Guizhou Province, Southwest China. To gain insight into the molecular responses during C. weiningensis adaption to cold stress, we investigated the transcriptome profiles and physiological changes of C. weiningensis leaves under chilling stress (4 °C) and freezing stress (-4 °C) conditions. Comparison with transcriptomes of C. weiningensis seedlings grown at room temperature (20 °C), 23,039 and 19,271 differentially-expressed genes (DEGs) were identified under chilling and freezing conditions, respectively. A total of 8907 DEGs overlapped for the 4 °C and -4 °C treatments. Common DEGs were mainly involved in signal transduction pathways, transcription factor regulation, photosynthesis pathways, fatty acid metabolism, biosynthesis of osmolytes and aquaporin, and antioxidant systems. Most DEGs associated with photosynthetic systems were down-regulated under cold stress, but the expression levels of most DEGs associated with sugar metabolism, aquaporin, peroxidase (POD), and glutathione S-transferase (GST) activities were up-regulated. In addition, physiological indicators reflected the gene activity associated with the RNA-sequencing findings; exposure to cold stress caused cell membrane damage, and a decrease in the chlorophyll content (Chl) and net photosynthetic rate (Pn). However, cold stress increased antioxidant enzyme activity (POD and GST), aquaporin activity, and soluble sugar content as adjustments to cold stress. Our studies identified key cold response pathways present in C. weiningensis, which will inform the planting of C. weiningensis in alpine mountainous areas and will facilitate further exploration of new candidate genes for chilling and freezing tolerance for the breeding of tea-oil tree cultivars.