| Soil salinization has become an important global resource and environmental problem.NaCl is the most common and widely distributed salt in saline soils.Plant metabolites are the result of the interaction between genes and the environment,and they are also the contributors to the special physiological and ecological functions of plants in specific environmental conditions.The halophytes,which possess a series of special survival strategies under the salt environment after they evolved specific salt tolerance mechanisms during the long-term evolution,are ideal systems for studying and dissecting the salt-tolerance metabolism mechanism and molecular regulation mechanism.Nitraria sibirica Pall.,a shrub plant belonging to Nitraria L.genus of Zygophyllaceae family.It is a relict plant of the Tertiary Period and typical salt-dilute halophytes which has strong salt-alkali resistance and drought resistance ability.However,the molecular and physiological metabolic mechanism of N.sibirica response to salt stress remain unclear.This research intends to use N.sibirica leaves treated with Na Cl as the studying materials.Based on the physiological response,high-throughput sequencing technology and advanced GC-TOF/MS techniques will be used to study transcriptional and metabolic changes of N.sibirica in response to salt stress.The correlation network of differential genes and differential metabolites were determined by association analysis of transcriptome and metabolome.Explains the molecular and physiological metabolic mechanisms of N.sibirica to salt stress.Main results for this study are as follows:（1）N.sibirica enhances the adaptability of salt stress by increasing the contents of osmoregulation substance and endogenous hormones ABA and GA.The content of soluble sugar in N.sibirica leaves decreased first and then increased with the prolongation of treatment time.When dealing with 3d,the soluble sugar content gradually began to increase.In the initial stage of NaCl treatment,the soluble sugar content gradually decreased with increasing treatment concentration,while the soluble sugar content gradually increased with increasing treatment concentration after 3 days of NaCl treatment.The content of proline and amino acids have a similar varying tendency.The proline and amino acids content increased with increasing treatment concentration.The content of proline and amino acid showed a trend of increasing first and then decreasing with the prolonging of treatment time,and it reached at a maximum in3d.The contents of the main endogenous hormone abscissin（ABA）and gibberellin（GA）was basically consistent with the different NaCl treatment conditions;with the increase of treatment concentration,ABA and GA content also gradually increased.With the prolongation of treatment time,the contents of ABA and GA also showed a increase and then decreased slightly,and there was a maximum in the treatment of 3d.The content of auxin（IAA）gradually decreased with the increase of treatment time.The content of IAA increased first and then decreased with the increase of concentration,and IAA content was highest in 100 mmol L-1NaCl treatment.（2）N.sibirica can improve the adaptability of salt stress by synergy of the genes which related to signal transduction,amino acids,organic acids,and sugar metabolism.Transcriptome sequencing of 9 samples from three treated N.sibirica leaves were performed on the Illumina HiSeq 2000 sequencing platform.A total of 72.21G clean reads were obtained,and 205,540transcripts and 126059 genes were obtained after splicing.Gene function annotations revealed that 91099（72.26%）unigenes were annotated in at least one database.According to the difference expression analysis of unigene,a total of 1337 differentially expressed genes were found between 100 mmol·L-1 NaCl treatment and unsalted treatment.And a total of 526differentially expressed genes were found between 400 mmol·L-1 NaCl treatment and unsalted treatment.The differentially expressed genes between 100 and 400 mmol·L-1 NaCl and unsalted treatment showed significant enrichment in GO terms such as binding,cell wall,extemal encapsulating structure,extracellular region and nucleotide binding.KEGG enrichment analysis found that NaCl treatment had a significant effect on the metabolic pathways in N.sibirica leaves,which mainly including plant-pathogen interaction,amino acid metabolism of the beta alanine,arginine,proline and glycine metabolism,carbon metabolism of glycolysis,gluconeogenesis,galactose,starch and sucrose metabolism,plant hormone signal transduction and spliceosome.（3）N.sibirica enhances its adaptability to salt stress by increasing the content of metabolites.which through the enhancing of amino acids metabolism and TCA cycle.At 3d treatment with different concentrations of NaCl,a total of 619 effective peaks were detected in extracts of N.sibirica leaves.PCA analysis showed that 100 mmol·L-1 NaCl treatment had no significant difference with unsalted treatment,but 400 mmol·L-1 NaCl treatment could be clearly distinguished from unsalted treatment.OPLS-DA analysis showed a clear distinction in different treatment concentrations.According to the VIP score of OPLS-DA and P value of t-test,a total of 10 and 34 differential metabolites have been selected betwen the comparison of100 mmol·L-1 NaCl treatment vs unsalted treatment and 400 mmol·L-1 NaCl treatment vs unsalted treatment,respectively.Differential metabolites are mainly amino acids（proline,aspartic acid,methionine,etc.）,organic acids（oxaloacetic acid,fumaric acid,nicotinic acid,etc.）and polyhydric alcohols（inositol,ribitol,etc.）,etc.The contents of alanine,asparagine,glutamine,glycine,proline,xylose,sucrose,mannose,oxaloacetic acid,malic acid in major metabolic pathways increased significantly under 400 mmol·L-1 NaCl treatment.KEGG annotation and enrichment analysis showed that 100 mmol·L-1 NaCl treatment had a greater effect on the sulfur metabolism,cysteine and methionine metabolism in N.sibirica leaves,while various amino acid metabolism,TCA cycle,photosynthetic carbon fixation and sulfur metabolism and other metabolic pathways have been significantly affected by 400 mmol·L-1NaCl treatment.（4）Correlation analysis of differential genes in transcriptome and differential metabolites in metabolome have found that the gene expression of AMY2,BAM1 and GPAT3 increased at upstream transcriptional regulation,increased the activity of amylase,which promoted the starch hydrolysis in the metabolic level and beneficial to the downstream metabolite synthesis such as L-Cysteine and 2-Aminophenol,etc.under 100 mmol·L-1 NaCl treatment.While under400 mmol·L-1 NaCl treatment,ASP1 expression enhanced promotes the synthesis of amino acids and their derivatives.The up-regulated expression of CML38 can activate multiple stimulatory signals,which can make the expression of stress-related genes and regulate the synthesis of proteins and metabolites.The up-regulated expression of RPL4 can promote the synthesis of proteins and enzymes.In conclusion,this study has based on the physiological basis of salt tolerance of N.sibirica,determined the differential genes and differential metabolites in N.sibirica leaves,and analyzed the transcriptional regulatory and physiological metabolic mechanism under Na Cl treatment.The study have found that the genes of AMY2,BAM1,GPAT3,ASP1,CML38 and RPL4 and the metabolites of L-cysteine,proline,4-aminobutyric acid and oxaloacetate played an important role in N.sibirica salt tolerance control.This is a further improvement of the salt tolerance mechanism of N.sibirica,and it will provide a theoretical basis and technical support for treatment of saline-alkali soil and the cultivation of halophytes. |
PDF Full Text Request