Study On Mechanism Of Medicago Falcata Adapting To Saline-alkali Stress Based On Metabolomic And Transcriptomic Analyses

Medicago falcata has excellent traits such as cold resistance,drought tolerance and saline-alkali resistance,and it has a powerful gene pool for forage breeding.In order to study the response mechanism of Medicago falcata to saline-alkali stress,metabolites and genes closely related to saline-alkali resistance,as well as related metabolic pathways,were excavated.In this experiment,Medicago falcata at seedling stage was used as the experimental material,and it was subjected to saline-alkali stress with different concentrations(0,50,100m M).The morphological and physiological indexes of seedling roots were determined.The differential metabolites and differential genes of seedling roots were analyzed by liquid mass spectrometry(LC-MS)and transcriptome sequencing technology,and bioinformatics analysis was conducted.The main results are as follows:The analysis of the response of Medicago falcata to 0、50 mm、100 m M salt concentration showed that the plant height,stem thickness,above-ground biomass and underground biomass decreased with the increase of the salt concentration,and the root system vitality and photosynthetic characteristics increased with the salt concentration.The content of Na~+,Pro,and soluble sugar increase with concentration of the saline solution.Metabolome analysis of Medicago falcata root showed that 479 different metabolites were obtained,among which biosynthesis of secondary metabolites,biosynthesis of unsaturated fatty acids,degradation of lysine and biosynthesis of flavonoid played an important role in saline-alkali stress.Transcriptome sequencing results showed that a total of 1.26×108 Clean reads were obtained,and 71,062Unigenes were obtained after comparison.The number of bases with mass value greater than or equal to 30accounted for more than 94.92%of the total number of bases.AP2/ERF-ERF,WRKY,BHLH and C2H2transcription factor families have important regulatory effects on Medicago falcata under saline-alkali stress.A total of 1717 differentially expressed genes,including 875 up-regulated genes and 842 down-regulated genes,were identified by expression analysis of roots.Functional enrichment analysis of GO and KEGG indicated that plant hormones,phenylpropanes,cysteine,methionine,glutathione and other metabolism-related pathways played a key role in saline-alkali stress.The results of association analysis between metabolome and transcriptome found that the key metabolic pathways of roots in response to salt-alkali stress are enhancement of phenylalanine metabolism,diterpenoid biosynthesis,isoquinoline alkaloid biosynthesis,and cysteine and methionine.Group and associated metabolic transcriptome analysis it was found falcata root key metabolic pathways in response to salinity stress is enhanced phenylalanine metabolism diterpenoid biosynthesis,isoquinoline alkaloids and cysteine and methionine biosynthesis.In this study,we studied the morphological and physiological responses of Medicago falcata seedlings under mixed salt-alkali stress,as well as the metabolome and transcriptome analysis of the seedling roots in response to stress,and the following conclusions were obtained:(1)Morphologically,mixed salt-alkali stress reduces photosynthesis,reduces organic matter and energy required for plant life activities,and affects the growth and development of alfalfa seedlings.The toxic effect of high concentration of Na+will destroy the structure and function of cells.Medicago falcata resists osmotic stress damage through K+efflux,and maintains osmotic balance through the accumulation of osmotic adjustment substances proline and soluble sugars.Medicago falcata has good resistance to complex salt and alkalinity.(2)The most critical metabolic pathway of alfalfa is the biosynthesis of diterpenoids.Including three genes GA20ox,GA2ox,Os KS1.GA20ox encodes GA20 oxidase,which is a degrading enzyme responsible for degrading C20 gibberellins;GA2ox encodes gibberellin 2β-dioxygenase,which inactivates gibberellins.The Os KS1 gene encodes endo-kaurene synthase(KS).KS is sensitive to gibberellin and is involved in the second reaction of gibberellin biosynthesis.In this experiment,GA20ox and GA2ox genes were up-regulated,and Os KS1 gene was down-regulated,which inhibited the growth and development of roots.