Physiological Response And Transcriptome Analysis Of Saposhnikovia Divaricata Under Drought Stress

Drought has a negative impact on plant growth and crop productivity around the world.Understanding the molecular mechanism of drought response through molecular techniques is of great significance to improving drought resistance.Saposhnikovia divaricata(Turcz.)schischk is widely distributed in Northeast Asia.Its dried roots are used as Chinese herbal medicine and have high medicinal and edible value.We find that Saposhnikovia divaricata has drought tolerance in production practice,but the understanding of its drought resistance mechanism is still in the primary stage.In order to decipher its response mechanism to drought and screen drought resistant genes,physiological and transcriptomics analysis were carried out.In this study,we used Saposhnikovia divaricata seedings as experimental material,through short-term continuous water stress treatment,which lasted for a total of 16 days,and then rewatering.The results of the study are as follows:After 8 days of drought,the fresh / dry weight of shoot increased significantly.After 16 days of drought,root diameter reached the maximum and root fresh / dry weight increased significantly.The results showed that Saposhnikovia divaricata had strong drought tolerance,and it could still maintain good growth condition under short-term drought.Drought stress induced the accumulation of antioxidant enzymes activities such as superoxide dismutase,peroxidase and ascorbate peroxidase.The results showed that drought induced oxidative damage of plants,and Saposhnikovia divaricata activated antioxidant system to repair the damage,thus responding to drought.Sequencing of the transcriptome of the Saposhnikovia divaricata root system produced a total of 167,447 unigenes with an average length of 807.49 bp.Among them,89,784 genes were annotated through the comparative database.A total of 9904 differentially expressed genes were identified between control plants and drought plants.Cluster analysis showed that most of the genes were down regulated under drought stress,especially during 12～16 days of drought.The down-regulated processes include the zeatin biosynthesis and carotenoid biosynthesis related to hormone synthesis,plant hormone signal transduction,terpenoids biosynthesis pathway,and phenylpropanoid biosynthesis and flavonoid biosynthesis related to secondary metabolism.Up-regulated genes are significantly enriched in carotenoid biosynthesis,α-linolenic acid metabolism,linoleic acid metabolism,starch and sucrose metabolism and other pathways.The expression of differentially expressed genes related to the removal of reactive oxygen species is also affected by drought stress.35 drought-induced transcription factor families were identified,and 541 transcription factors showed differential expression under drought stress.Comprehensive analysis of differential genes showed that the response of Saposhnikovia divaricata roots to drought was not a single metabolic process,but multiple metabolic pathways interacted,forming a complex regulatory network,thus promoting the adaptation of Saposhnikovia divaricata roots to drought stress.The expression patterns of 16 differentially expressed genes were analyzed by fluorescence quantitative PCR,and the accuracy of sequencing results was verified.The results showed that the two methods were highly correlated,which confirmed the reliability of RNA-seq sequencing results.In this study,we sequenced the transcriptome of Saposhnikovia divaricata roots under different drought stress for the first time.The physiological,biochemical and transcriptome results related to drought showed the dynamic response of Saposhnikovia divaricata to drought and recovery,which provided valuable information for better understanding the mechanism of drought tolerance and laid a good foundation for its follow-up research.