Study Of Genotypic Difference And Mechanism Of Drought Tolerance In Wild Barley From Evolution Canyon

Drought is one of the major environment factors limiting crop growth and reducing crop production,therefore affecting global food supply.Barley is ranked the fourth largest cereal crops,characterized by its high drought tolerance and wide adaptability.Wild barley,ancestor of cultivated barley,is a valuable genetic resources for barley improvement.It is important to understand the mechanism of drought tolerance in barley.In this study,we used wild barley derived from "Evolution Canyon",Israel,to study the difference mechanism of drought tolerance in metabolic and transcriptome level.The results are as follows:1.Mechanisms of amino acid content in response to drought stress in wild barley.In this study,we analysed the changes of amino acid contents in response to drought stress and identified a total of 18 amino acids after drought stress in flag leaves.The results showed that the content of alanine,valine and leucine of pyruvate family and histidine were significantly increased under drought stress.It was presumed that the glycolysis pathway and the decomposition of carbohydrates were enhanced.Threonine and lysine of the aspartic acid family and proline in the glutamate family were significantly increased in both groups,suggesting that the tricarboxylic acid cycle was enhanced.The proline content was dramatically increased after drought treatment,and significantly higher than other amino acids.Proline could be used as an osmoregulation substance,maintaining cell osmotic potential and relieving damage of water stress.GABA,which is another important amino acid,was significantly increased only in the ES group.The results indicate that there were significant differences in response to drought stress at the amino acid level between the wild barley genotypes from AS and ES.2.Mechanisms of metabolic content in response to drought stress in wild barley.In order to understand the mechanisms of metabolic content in response to drought stress in wild barley,we analysed the leaf metabolites and identified forty-five metabolites.More than 20 metabolites were significantly increased under drought stress.Fructose,glucose,raffinose,sucrose,ribitol,succinic acid,fumaric acid,threonic acid,shikimic acid,citric acid and galacturonic acid were significantly increased both in AS and ES genotypes.Most of them are carbohydrates and organic acids which may be generated in response to drought stress.Among them,succinic acid,fumaric acid and citric acid are involved in the tricarboxylic acid cycle,which indicate the enhancement of tricarboxylic acid cycle under drought stress.Fructose,raffinose,sucrose can be used as osmoregulation substances to alleviate water stress.The results indicate that wild barley might alleviate drought stress by enhancing tricarboxylic acid cycle and accumulation of soluble sugar.3.Mechanisms of transcriptome in response to drought stress in wild barley.Based on the results of metabolites analysis,RNA-Seq technique was used to study the drought-tolerance mechanism of barley at transcriptional level.We found that drought stress significantly affect the function of cell components such as thylakoid lumen,plastid thylakoid lumen and chloroplast thylakoid lumen,which related to photosynthesis and other physiological processes.The genes related to biological process,such as shoot development,monosaccharide catabolism and glucose catabolism,were significantly down-regulated after drought treatment.Glucose might be used to synthesize raffinose,sucrose,betaine and other osmolyte,therefore alleviating drought stress.The genes of symporter activity,soluble cation symporter activity,oxidoreductase activity,and inorganic anion transmembrane transport activity were significantly up-regulated under drought treatment.The expression of transporter-related genes was significantly up-regulated,which may be related to the transport of osmoregulation substances.The present study indicated that wild barley might enhance drought tolerance by synthesizing osmolyte and increasing transporter and oxidoreductase activity.