| The greenhouse vegetables planting area in Hebei province has been expanding in recent years.However,the soil salinization in greenhouse soil is becoming serious,that mainly leaded by excessive and inappropriate use of chemical fertilizer.The soil salinization greatly limits the growth,yield and quality of vegetables.Using plant growth-promoting rhizosphere bacteria(PGPR)is proved as an alternative and environmentally friendly method to increase the salt tolerance ability and promote growth of plants under salt stress.In this study,24 strains of biocontrol bacteria preserved in our laboratory were evaluated for tomato growth promotion under salt stress.Results showed that Bacillus subtilis strain NCD-2 could significantly promote the growth of tomato.Effects of strain NCD-2 on the activities of stress-related enzymes in tomato plants were investagated,and effects of strain NCD-2 on the genes expression of tomato plants were also analyzed using transcriptome technology.In addition,the influence of strain NCD-2 on the rhizosphere microbial community structure of tomato was also determined by high-throughput sequencing technology.The influence of strain NCD-2 on the rhizosphere microbial functional diversity of tomato was determined by Biolog-ECO technology.The main results of this study are as followings.1.The tomato growth promotion of 24 bacterial strains with biological control abilities were evaluated under salt stress.B.subtilis NCD-2,B.subtilis HMB27703,B.amyloliquefaciens HMB27688,B.amyloliquefaciens HMB27633,B.amyloliquefaciens PHODB35 showed stronger growth promotion abilities when compared to other bacterial strains,and strain NCD-2 showed the strongest growth promotion effect.The stem length,stem fresh weight,dry weight,root fresh weight,dry weight of tomato seedlings were increased by 26.70%?24.90%?23.78%?22.49%?24.22%respectively,after treated with strain NCD-2.2.The growth promotion effect of strain NCD-2 was evaluated under 100 mM,200 mM,and 400 mM NaCl,respectively.Results showed strain NCD-2 could promote tomato growth under different concentrations of NaCl.Moreover,the most significant growth promotion effect was achieved under 100 mM salt sress,and the tomato stem lengh,fresh weight and dry weight of stem,root fresh weight and dry weight of tomato seedlings were increased by 16.86%,18.96%,21.32%,10.50%,23.99%after treated with strain NCD-2.The activities of POD,SOD,CAT as well as ABA concentration in tomato plants were increased by 56.18%,50.45%,29.55%and 34.60%,respectively,after treated with strain NCD-2.3.The gene expression profile of tomato after treated with strain NCD-2 under 100 mM NaCl stress was analyzed using transcriptome technology.Results showed that 216 genes were up-regulated and 96 genes were down-regulated after treated with strain NCD-2.Among them,catalase gene,divinyl ether synthase gene,linoleic acid-lipoxygenase gene and other genes associated with stress-related enzymes were up-regulated by strain NCD-2.GO analysis of differentially expressed genes was performed,and the result showed the differential genes were mainly involved in oxidoreductase activity,tetrapyrrole binding,iron ion binding,catalytic activity and cofactor binding.KEGG pathway analysis showed the differentially expressed genes mainly involved in plant hormone signal transduction,MAPK signal transduction pathway,starch and sucrose metabolism.Using Pfam database,the domains of differentially expressed genes were analyzed and results indicated these genes mainly involved CYP74 family,glycosidehydrolase family,short chain dehydrogenase/reductase family and VQ protein.It was speculated that these domains played an important role in salt tolerance of tomato.Strain NCD-2 could increase the expression of ERF transcription factor,which had been proved to be involved in resistance to abiotic stress.4.Effects of strain NCD-2 on microbial community structure of tomato rhizosphere under 100 mM NaCl were analyzed by high-throughput sequencing technology.Analysis of bacterial community composition showed that the relative abundances of Proteobacteria,Actinobacteria,Firmicutes and Blastomonas in tomato rhizosphere were increased by 6.08%?8.19%?14.11%?4.70%respectively,after treated with strain NCD-2.The relative abundances of Arthrobacter,Bacillus,Sphingosinomonas and Microchirobacter were increased by 5.54%?31.80%?23.39%?23.08%respectively,after treated with strain NCD-2.For fungal community composition analysis,the relative abundances of Mortierella,Streptomyces and Cryptomycetes were increased by 345%,154%,921%respectively,after treated with strain NCD-2.The relative abundance of Mortierella was increased by 246%,and Aspergillus,Fusarium was decreased by 66.70%and 20.14%after treated with strain NCD-2 respectively.According to the results of microbiome,it was speculated that increasing the number of beneficial bacteria such as Arthrobacter,Bacillus,Sphingomonas,Microvirga and reducing the number of pathogenic fungi such as Aspergillus and Fusarium might be one of the reasons for promoting the tomato growth of strain NCD-2 under salt stress.5.BioLog-ECO plate was used to determine the effect of strain NCD-2 on the functional diversity of rhizosphere microbial community of tomato under 100 mM NaCl.Results showed strain NCD-2 significantly improved the utilization of six kinds of carbon sources,comparatively,carboxylic acid and carbohydrate had the highest utilization effect.Further analysis showed strain NCD-2 treatment improved the utilization of three types of carboxylic acid carbon sources such as itaconic acid,y-hydroxybutyric acid and methyl pyruvate,as well as three carbohydrate carbon sources such as D-mannitol,D-xylose and ?-D-lactose under the stress of 100 mM NaCl.It was inferred that the carbon source utilization types of rhizosphere microorganisms were changed by changing the community structure of tomato rhizosphere microorganisms after treated with strain NCD-2. |
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