Tag-based identification of differentially expressed genes under cold and freeze stress in seabuckthorn (Hippophae rhamnoides L.)

Purpose: Tag-based approach for global gene expression analysis has been revolutionised with the advent of next generation sequencing (NGS) technology. The aim of the present study is to present comprehensive view of differentially expressed genes under cold and freeze stress in seabuckthorn (Hippophae rhamnoides L.) Methods: DeepSAGE, a tag based approach, was used to identify differentially expressed genes under cold and freeze treatments in seabuckthorn (Hippophae rhamnoides L.). The 30 days old plantlets, at six leaves stage, were subjected to cold stress (CS) at 4°C and freeze stress (FS) at -10°C treatment for 6 hr. The seedlings grown at 28°C were taken as control (CON). Total RNA from all the three samples was isolated. Illumina Gene Expression Sample Prep Kit and Solexa Sequencing Chip (Flowcell) were used for tag preparation and the main instruments used for sequencing included Illumina Cluster Station and Illumina HiSeqTM 2000 System. Bioinformatics analysis resulted in to high number of differentially expressed genes under cold and freeze stress. Results: 36.2 million raw tags including 13.9 million distinct tags were generated from three leaf tissue libraries (control, cold stress and freeze stress). After removing low quality tags, 35.5 million clean tags including 7 million distinct clean tags were obtained. In total, 11922 differentially expressed genes (DEGs) were identified including 6539 up regulated and 5383 down regulated genes. Conclusions: DeepSAGE data of seabuckthorn provided useful resource and reference dataset for further functional genomics analysis in seabuckthorn and other important crops. The present study implicated a large number of genes with different biological functions expressing differentially in response to cold and freeze stress treatment. Isolation and further characterization of these genes will help researchers in understanding their role in cold and freeze tolerance in seabuckthorn and may provide important gene resources to be exploited for the development of stress tolerant crop plants in future. Overall design: Differential gene expression profile of seabuckthorn (Hippophae rhamnoides L.) under cold and freeze stress was generated through DeepSAGE. Tags were generated using mRNA isolated from all the three, control, cold stressed and freeze stressed leaf tissues samples. Tags generated were further sequenced using Illumina Cluster Station and Illumina HiSeqTM 2000 System.