| Microorganisms play an important role in the material circulation,energy flow and signal transduction exchange in environment.Soil microorganisms affect the growth and development of plants and their health through direct or indirect interactions with the underground parts of plants.At the same time,plant influence the soil microbial community structure by secreting root secretions and metabolic activities of border cells.Interactions between soil microorganisms and plant roots are mainly concentrated in the rhizosphere.Structure of rhizosphere microbial communities are the result of the interaction between soil environment and plant root metabolism.Cotton is an important economic crop,and most of the major cotton-producing areas in China are cotton continuous cropping models,which have affected the structure of microbial communities in cotton fields,significantly reduced biodiversity,and increased the incidence of soil diseases.Cotton yield is greatly reduced by pests and diseases under this model.Soil-born pathogenic fungi are the main pathogens of cotton.However,understand of the dynamics of these pathogens and microbial community structures in the rhizosphere soil at different developmental stages of cotton were limited.By fully understanding cotton rhizosphere microbial community structure and regulation mechanism,we can control the rhizosphere microbial community by adjusting the root environment of cotton,so as to inhibit the colonization of soil borne pathogens,reduce the incidence of soil borne diseases,promote the growth and development,and increase the yield of cotton.In this study,the structure of microbial community and the gene express condition of plant root system were studied:Two cultivars of cotton were cultivated: upland cotton(Gossidium hirsutum cv.TM-1)and Island Cotton(G.barbadense cv.Hai 7124)for the material.Use the high-throughput sequencing technology to study the changes in the structure of bacterial and fungal communities in the rhizosphere in two different soil environments in three different developmental stages.The results indicate that:1.The dominant bacterial phyla in the cotton rhizosphere bacterial community are Proteobacteria,Acidobactria,Bacteroidetes,Planctomycetes,Actinomycetes,Verrucomicrobia.Among them,the relative abundance of Proteobacteria was highest than that of other bacteria.In addition,the abundance the Proteobacteria,Planctomycetes,Firmicutes,Acidobacteria,and Cyanobacteria were greatly affected by the cotton root.In different soil types,the effects of cotton roots on soil bacteria are different.The alpha-diversity of rhizosphere bacteria was reduced in nutrient soil,and increased in field soil that cotton continuous cropped,compared with bulk soil.And the β-diversity between the nutrient soil samples was higher than the β-diversity between the samples of field soil.There are significant differences in the structure of rhizosphere bacterial communities between different developmental stages.The α-diversity of the two species in the nutrient soil and the Island cotton in the field soil in the budding stage were higher than that of the other two developmental stages,and each developmental stages has its typical orders,the seedling stage was Xanthomonadales,the budding stage was Rickettsiales,Opitutales,Pseudomonadales,and the flowering stage was Solibacterales.Among the factors that affect the structure of cotton rhizosphere microbial community,the soil type has the greatest effect on cotton rhizosphere bacteria,which was contribute about 54.03 % of rhizosphere bacterial community change,significantly higher than the other two factors(developmental stage: 19.23 % and genotype: 12.39 %).2、The dominant fungal phyla in both soil types are Ascomycota,Basidiomycota and Zygamycota.The rhizosphere fungi greatly affected by cotton was mainly distributed in Basidiomycota.There were significant differences in the structure of rhizosphere fungal communities between different soil types,suggesting that soils were the key factors in determining rhizosphere fungi communities.The results of fungal diversity analysis of bulk soil showed that the α-diversity of fungal community in nutrient soil was significantly higher than that of bulk soil,but the α-diversity of rhizosphere fungi community in nutrient soil was lower than in field soil.In addition,the pathogenic fungal relative abundance of bulk soil was higher in field soil than in the nutrient soil,but lower in field soil than in nutrient soil for rhizosphere.Developmental stage was another important factor affecting the structure of rhizosphere fungal community.Each developmental stage has its specific dominant genus.In addition,pathogenic fungal have the developmental stage specificity.Relative abundance of Rhizoctonia and Streptococcus in the seedling stage,Thanatephorus,Trichoderma,Gibberella,and Fusarium in budding stage was increased significantly in field soil.In the nutrient soil,relative abundance of the Rhizoctonia in budding stage,and the Gibberella in flowering sage increases significantly in rhizosphere soil.It was assumed that the infection rate of these diseases will be higher in the corresponding stages.Our study reveals the dynamics of bacterial and fungal community composition in cotton rhizosphere,which was determined by soil and affected by the selection of cotton root.The study of changes in the structure of microbial communities of rhizosphere under different conditions lay the foundation for regulation of the growth and development of cotton by artificially regulating the community structure of soil microorganisms,improving the defense ability of cotton and even other crops that are susceptible to soil diseases,reduce the incidence of cotton diseases and increase cotton production.Another part of this study was characteristics of cotton root border cell(BC)and transcriptional analysis of the cotton root tip(RT)and root boder cells under normal and stress conditions.The results are as follows:1、The number and size of cotton border cells of different varieties were calculated and found that the number of border cells was different in different varieties.There was no significant correlation between the number and size of cotton and the characteristics of cotton varieties.We have selected Lumianyan 37 as the material for this experiment.2、There were significant differences between the transcriptome of border cells and root tip.Compared with the root tip cells,the secondary metabolic level of the cotton border cells was higher,and the expression of gene related to the stress response was maintained at a higher level.In the root tip,different express gene that keep higher level compared with that in border cells are mostly related to the growth of plants and hormones such as cell division and elongation.It was assumed that this transcriptome difference between root border cells and root tip was related to the function of defense of border cells.3、The protect mechine of BC to RT were singinificantly different under different stress conditions.Border cells response to salt stress through elevate the pathway of glutathione metabolism,the synthesis of secondary metabolites,the degradation of limonpinene,the biosynthesis of terpenoids and terpenes,the synthesis and metabolism of phenylpropanoids,the synthesis and metabolism of sugars,glycerides,the metabolism of lipids such as glycerides and methyl butyrate,the biosynthesis of carotenoids,and glyoxyuronic acid and dicarboxylic acid metabolism.And respondse to V991 stress by improving the synthesis of secondary metabolites,the metabolism of glutathione,the degradation of limonene and pinene,synthesis of diaryl heptane and ginger horseradish compounds,the synthesis of flavonoids,the biosynthesis of carotenoids,the biosynthesis of phenylpropanoids.Studies on transcriptome of cotton RT and BC under biotic and abiotic stresses revealed differences in metabolism and stress response between cotton RT and BC.The transcriptome analysis of cotton RT and BC under different stress conditions laid a foundation for studying the effects of root exudates and BC on cotton rhizosphere microorganisms.Innovations of this study:1、This is the first time,high-throughput sequencing technology was used to study the microbial community structure in cotton rhizosphere,and systematically study the influence of each factors for cotton rhizosphere microbial community and their contribution to the changes of community structure.Predicting the infection of pathogenic fungi at different developmental stages has potential application value for the prevention of soil-borne diseases in agricultural production.2、It is the first time to study the difference between the root tip and the root border cells of cotton at the transcription level.The transcriptome differences of cotton root tip and border cells under normal and stress conditions were analyzed.The protective mechanism of the border cells on the root tip and the response difference between the root tip and the border cells to biotic and abiotic stresses were analyzed.3、A cotton border cell culture and collection system was established.The system can be used for the cultivation,biotic and abiotic stress treatment,and collection of border cells.The experimental results based on this system are low cost,high controllability,stable processing environment,and high repeatability,which lays a foundation for future research. |
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