The Study Of The Response And The Molecular Mechanisms Of Astragalus Membranaceus BGE.VAR.Mongoliclus(BGE.)to Drought Stress

The shortage of the water resource is a common phenomenon in Northwestern China, which seriously affects the development of the local economy and production. It is important to search for drought-adapted plants and study the plants response to drought stress. Astragalus membranaceus Bge. var. mongolicus (Bge.) Hsiao (A. mongolicus) is a traditional Chinese herb, the roots is used in medicine. At present, it is primarily cultivated on a large scale in the northern and northwestern regions of China. In this study, we used A. mongolicus as experimental material to study the effects of drought stress on the growth, physiological and biochemical responses and secondary metabolite accumulation of A. mongolicus. And we combined transcriptomics (Illumina Hiseq 2000) and metabolomics (1H-NMR) to investigate how A. mongolicus responded to drought stress. Additionally, we studied the effects of moderate drought stress on the growth and the quality of A. mongolicus, and studied the effects of salicylic acid (SA) on drought resistance of A. mongolicus, which was sprayed on the leaves. The results of the present study are as follow:1. The dried soil reduced the relative water content (RWC) of the leaves and biomass during the 14 days of progressive drought stress. Mild and moderate drought stress enhanced some antioxidative enzyme activity, the content of proline and soluble sugar content, but antioxidative enzyme activity was limited by severe stress. A certain degree of drought stress can enhance accumulation of astragaloside IV, calycosin-7-O-β-D-glycoside, ononin, calycosin and formononetin.2. Metabolomics demonstrated that the metabolic processes were significantly affected by drought stress. PCA analysis demonstrated that the sucrose, proline, and malate metabolites contributed greatly to the separation. Strikingly, proline was increased by almost 60-fold under severe stress compared to the control. Some backbone pathways, including glycolysis, tricarboxylic acid (TCA) cycle, glutamate-mediated proline biosynthesis, starch and sucrose metabolism, were significantly affected by drought.3. Transcriptomics demonstrated that the differential expression of a large fraction of the transcriptome after drought stress. Compared with control, there are 18,292,15,085,20,986 differentially expressed genes (DEGs) in mild stress, moderate stress and severe stress.The expression of P5CS, PDH, MDH, zinc finger proteins genes and cytochrome P450s genes were different during drought stress, which are more likely to determine tolerance to drought.4. In moderate drought stress stage, the biomass of A. mongolicus was decreased in two different varieties, but the content of astragaloside IV, calycosin-7-O-β-D-glycoside, ononin, calycosin and formononetin these secondary metabolites were increaed at different levels.5. After spraying a certain concentration of SA on leaves, on the 10th day, compared to the drought group, the antioxidant enzymes activity was enhanced, the content of osmotic agents was significantly increased.The SA group has a higher leaves RWC, leaf water potential, chlorophyll content, and a lower electrolyte leakage (EL) and malondialdehyde (MDA) content than the drought group. It indicated that SA had a certain effect on the drought resistance of A. mongolicus.