| Soil salinization is one of the main abiotic stress factors affecting crop growth and development,limiting crop yield and causing serious economic losses.Screening salt-tolerant mutants,mining candidate genes for salt-tolerant regulation and cultivating high-quality salt-tolerant mutants will be the key points of crop breeding,which are helpful for improving and utilizing saline and alkaline land.In this study,suitable and inheritable mutant(KFJT-3)screened by treating dry seeds of sweet sorghum(Wild type,WT)using carbon ions.The salt tolerance of KFJT-3 was higher than WT,and KFJT-3 can withstand 200 m M Na Cl stress.Through phenotypic observation,cellular level detection and physicochemical level research,we elucidated the KFJT-3 physicochemical factors associated with salt tolerance.Transcriptome sequencing and Untargeted Metabolomics high-throughput detection technology,comprehensively study the changes of KFJT-3 transcript level and metabolite level under salt stress,and explore key genes and metabolites of KFJT-3 in response to salt tolerance.Based on the research results of physicochemical properties and multi-omics analysis,the molecular mechanism of carbon ion-induced salt tolerance response of KFJT-3 was systematically described.The main results of our research are described as follows:(1)The 14-day-old sweet sorghum seedlings were cultivated in 200 m M Na Cl nutrient solution for 72 h,the plant height,root length and leaf length of WT decreased by 2.24%,6.56% and 4.94% respectively,while those of KFJT-3 decreased by 10.35%,6.08%,7.59%.Compared with the control group,WT showed that leaves withered from green to yellow,the color was obvious,the leaf tip was red.The number of lateral roots of WT was reduced the root length was shortened and the main root changed from yellow to red,and the color was fresh.Compared with the control group,KFJT-3 showed that the leaves changed from green to light yellow,the tip of the leaves changed red was not obvious.The root of KFJT-3 changed from yellow to light yellow,the number of lateral roots was reduced and the root length was significantly shortened.(2)The chlorophyll content,relative water content and photochemical efficiency of sweet sorghum under salt stress were determined.The results showed that compared with the control group,the Chl content of WT and KFJT-3 respectively decreased 51.50% and 10.56% and RWC respectively decreased 9.25% and 9.76%.After salt stress treatment,the difference between Fo,Fm,Fv/Fm,ETR and q P of KFJT-3 and WT were not significant,except NPQ,indicated that the light energy dissipated by KFJT-3 was much lower than WT.In order to cope with the lower energy utilization efficiency of the reaction center,WT needed to absorb more light energy and capture more energy,which was consistent with the determination of Chl content.(3)We compared with the leaf and root anatomical characteristics of sweet sorghum WT and KFJT-3 under salt stress.Under the light microscope,after salt stress treatment,the epidermal structure of WT leaves was seriously damaged,the cell structure was arranged,the intracellular chloroplast was massively outflowed,and only the cells around the leaf vein were relatively completed.The overall outline of the mutant KFJT-3 leaf cells was clear,and the mesophyll cells and vascular bundle sheath cells were shrunk,compact but intact.The root cell structure of WT and KFJT-3 was severely damaged.The epidermal cells and syllium cells of the WT root cells were relatively intact,the endothelial cells were severely damaged,and the cell contents were outflowed.The root cells of KFJT-3 were relatively intact.Intact,with severely damaged outer cortical cells.Under transmission electron microscope,after salt stress treatment,the stromal lamella and granulosa lamina were blurred and the number of starch granules decreased in WT leaf tissue while the stromal lamellar was obvious in KFJT-3 leaf tissue,while the granola plasmic layer was also blurred.Osmophilic granules were clear,and the number of starch granules was reduced.(4)The physiological indexes of sweet sorghum under salt stress were measured.The results showed that the relative conductivity,total protein content,MDA content,pro content,SOD enzyme activity,pod enzyme activity and cat enzyme activity of KFJT-3 root,stem and leaf were always higher than those of wt.Total protein content,MDA content,pro content,SOD enzyme activity,pod enzyme activity and cat enzyme activity were significantly different between KFJT-3 and WT in roots and stems,but not in leaves.It can be used as a reference index for the identification of salt tolerance traits of sweet sorghum.(5)To analyze the regulation mechanism of salt tolerance of KFJT-3 in sweet sorghum,the transcriptomes of WT and KFJT-3 in the control and experimental groups were sequenced.WT-0 VS WT-200,KFJT-3-0 VS KFJT-3-200,WT-200 VS KFJT-3-200 respectively detected 3220,4950,2562 differentially expressed genes.The results of KEGG pathway enrichment analysis showed that the differential genes of salt tolerance were mainly concentrated in photosynthesis-related and antioxidant-related metabolic pathways,including peroxidase metabolic pathway,glutathione metabolic pathway,and carbon fixation in photosynthetic organisms.In addition,the screened salt tolerance differential genes were verified by q RT-PCR,and the results were consistent with the RNA-Seq data.(6)Transcriptome-metabolome association analysis showed that 11 salt tolerance-related KEGG metabolic pathways were significantly enriched,and DEGs and DEMs were mainly enriched in antioxidant-related KEGG pathway.Antioxidant and salt tolerance-related gene expression analysis showed that KFJT-3 up-regulated the expression of phenylalanine lyase(4CL)and coumarin Co A ligase(PAL)genes in the phenylalanine metabolic pathway;glutathione metabolic pathway.The gene expression of glutamyltransferase(GGT1)was up-regulated,and the Cys-Gly metabolite was up-regulated;the gene expression of hydroxy acid oxidase(HAO)in the glycolic acid cycle was down-regulated. |
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