Study On The Response Mechanisms Of Foxtail Millet(Setaria Italica L.) Seedlings To Drought Stress Based On Transcriptome And Proteomics

Foxtail millet（Setaria italica L.）,belonging to the C₄crop,has the characteristics of drought resistance,soil barren tolerance,and strong adaptability in wide area.It is one of important and special agricultural crops in China,that maintains agricultural economic stability in arid and semi-arid areas.As an abiotic stress,drought seriously inhibits its growth and development,and restricts the improvement of yield.Therefore,it is of great significance to carry out molecular biology research on drought resistance of foxtail millet,to reveal the genetic background and molecular regulation mechanism of foxtail millet drought resistance,and to improve the drought resistance of foxtail millet varieties.In this study,two foxtail millet cultivars,the drought-resistant cultivar"Damaomao"（DM）and the drought-sensitive cultivar"Hongniangu"（HN）,were used as the experimental materials under the PEG6000-simulated drought stress at the seedling stage（three-leaf stage）.Physiological and molecular regulation mechanism of foxtail millet response to drought stress were studied by analyzing the physiological and biochemical parameters,and through the analysis of the expression patterns of the transcriptome and proteome between the treatments and the control.The main research results obtained are as follows:（1）When subjected to drought stress,the two foxtail millet varieties showed a decrease in leaf width,leaves turning yellow and wilted,above-ground biomass decreased significantly,root-shoot ratio increased,and the net photosynthetic rate（Pn）and stomatal conductance（Gs）were significantly inhibited.The content of chlorophyll a and b were both decreased significantly.The content of MDA,soluble sugar and proline continued to increase with the time course of drought stress.The content of ABA and JA increased significantly within 24 hours.Compared with the drought-sensitive variety HM,the root-shoot ratio and proline content of the drought-tolerant variety DM increased more,and the MDA accumulation level,RWC and chlorophyll content decreased less,indicating that the metabolic activity of the DM could be maintained at a certain level,and its drought tolerance is stronger than that of HN,which is consistent with the field observation data.（2）A total of 3,488 differentially expressed genes（DEGs）（1,644 up-regulated,1,844down-regulated）and 2,040 DEGs（1,311 up-regulated,729 down-regulated）were identified in the drought-tolerant variety DM and drought-sensitive variety HN,respectively.The two varieties co-expressed 919 DEGs（899 DEGs’expression pattern were the same,and 20were opposite）.These co-expressed genes were mainly involved in terms of stress tolerance、response to stimulus and response to heat.Compared with the drought-sensitive variety HN,drought stress promoted the related gene expression of glutathione metabolism,chlorophyll sythesis,ascorbic acid cycle,arginine and proline metabolism,flavonoid metabolism and oxidation-reduction metabolism in the drought-resistant variety DM.And drought stress promoted the soluble sugar metabolism and chlorophyll degradation metabolism of HN.（3）Under the drought stress,a total of 66 differentially expressed proteins（DEPs）were identified in the tested foxtail millet leaves.And 34 types of DEPs（23 up-regulations and 9down-regulations）were identified in the drought-resistant variety DM leaves,23 kinds of DEPs（12 kinds of up-regulation and 11 kinds of down-regulation）were identified in drought-sensitive variety HN.There were 9 kinds of DEPs were identified both in two varieties.These differential proteins were mainly involved in photosynthesis,glycolysis,TCA cycle,protein and amino acid metabolism,and stress-related protein metabolism.Drought stress significantly induced starch degradation metabolism and expression of glycolysis-related enzymes,and inhibited the expression of photosynthesis and TCA cycle-related enzymes in two cultivals.（4）The transcriptome-proteome correlation analysis showed that the expression of differential proteins（DEPs）in the proteome was positively correlated with the genes expression in the transcriptome,with a strong correlation.In DM,spillman rank correlation coefficient value is 0.0333,and Pearson product-moment correlation coefficient r value is0.6720.In HN,theρvalue is 0.0443 and r value is 0.5757.The correlation analysis between transcriptome and proteome showed that there were significant differences in the number and abundance of DEGs and DEPs,but the expression patterns and metabolic pathways were highly consistent under drought stress.（5）Under the drought stress,the physiological and biochemical responses and transcriptome response,proteome response of foxtail millet leaves had formed a broad and comprehensive net of regulation in photosynthesis,signal transduction,antioxidant regulation,hormone signaling,transcriptional regulation,osmotic regulation,basic substance metabolism.Comparing the two varieties,the drought resistance of the drought-resistant variety DM was getted by its effective biomass allocation mechanism,stronger ability of leaf water capacity and osmotic adjust,lower membrane lipid peroxidation and stronger hormone-mediated signal transduction.Drought stress could significantly induce the genes expression of glutathione metabolism,chlorophyll synthesis,ascorbic acid metabolism,arginine and proline metabolism,flavonoids metabolism and oxidation-reduction metabolism in the leaves of the drought-resistant variety DM.The increased expression of free amino acids synthesis related proteins and the stress-related proteins could effectively promote the anabolic pathway of key metabolites,and improve the osmotic adjustment,ROS detoxification,and cell water retention ability.