Mechanisms Of Phosphtate-solubilizing Rhizobacteria WS32 Promoting Wheat Growth And Phosphorus Absorption

To explore the interaction between the affinity phosphate-solubilizing bacteria WS32 and wheat,the mechanism of rhizosphere phosphate-solubilizing bacteria promoting wheat growth and phosphorus absorption was revealed.In this study,the phosphate-solubilizing and growth-promoting Pseudomonas fluorescens WS32 strain with specific affinity to wheat screened by our laboratory and wheat were used as affinity pair.By using the combined analysis method of transcriptome and metabolome,the differences in the transcriptional expression profiles of wheat plants inoculated with WS32 and unoculated wheat plants were studied,and the metabolites related to phosphorusolysis and growth-promoting function in WS32 were analyzed.The molecular mechanism of strain WS32 promoting wheat growth and phosphorus absorption was analyzed.Root bag experiment was used to study the effects of the affinity phosphate-solubilizing bacteria WS32 strain on wheat seedling growth,root development and phosphorus absorption.The results showed that the application of phosphate-solubilizing bacteria WS32 significantly promoted the fresh and dry weight of the aboveground part,root dry weight,phosphorus content of the leaves and available phosphorus content in the soil when wheat was grown for 25 d.The root scanner was used to analyze the growth indexes of wheat roots growing for 25 d.The results indicated that the root surface area and tips were significantly increased after the application of phosphate-solubilizing bacteria WS32 compared with the uninoculated ones.Transcriptomics analysis of the difference in transcriptional expression profiles between the roots of wheat plants inoculated with WS32 and uninoculated ones.The raw data was sorted and filtered,and the Q20 and Q30 values were above 85%.After the high-quality filtered data,the differential genes were screened to obtain 1485 significant differential genes in wheat roots,including 468 genes upregulated and 1017 genes downregulated.Annotating the differentially expressed genes according to the GO database and the KEGG metabolic pathway library.Differential genes can be classified into functional categories: phosphorus and other nutrient elements absorption,root hormone absorption and organic acid secretion,flavonoid signal recognition,membrane transcription and absorption,TFs regulation,defense and stress resistance.Eight genes were randomly selected from the significant difference genes to determine the relative expression of the differential genes by using the q RT-PCR method.The results showed that trends in changes in gene expression of the 8 genes was the same as the transcriptome sequencing results,which indicated that the sequencing results were reliable.Metabolites of WS32 were determined by LC-MS,and metabolomics was used to analyze the metabolites of the strain related to phosphate-solubilizing and growth-promoting functions.According to the results of the omics analysis,1580 metabolites were screened,and positive and negative ion metabolites were integrated and classified.WS32 strain can produce four organic acids,including aconitic acid,disodium malate,oxalic acid,and salicylic acid.These organic acids may help to dissolve and release the insoluble phosphorus in the soil,and then play a role in the absorption and utilization of phosphorus in wheat;the WS32 strain can also produce IAA,iron carriers,fatty acids,amino acids,vitamins and coenzymes,carbohydrate metabolites and other plant growth hormones and nutrients to provide hormones and nutrients for wheat growth to promote wheat growth.Furthermore,WS32 secretes mycinamicin,anticapsin,gentamicin A,oligomycin B,kanamycin 3’-phosphate and other antibiotics during the growth process,which can inhibit the invasion of pathogenic bacteria and enhance the disease resistance of wheat plant.To study the role of exopolysaccharide in mediating the mutual recognition of promoting bacteria with affinity and wheat,high speed centrifugation method was used to remove the exopolysaccharide of WS32.The WS32 strains with and without exopolysaccharide were reacted with wheat lectin,respectively,and it was found that the affinity of WS32 with lectin decreased,and the cells could not aggregate agglutinate after removing exopolysaccharide.The wheat roots were immersed in the bacterial solution of WS32 with and without exopolysaccharide,respectively.At the same time,the amount of adsorption of exopolysaccharide-deficient cells in the wheat roots was significantly lower than that of cells with exopolysaccharide.The results showed that the exopolysaccharide of the bacteria play an important role in the process of recognizing each other between the growth-promoting strains and wheat plant,and thus in the process of adsorption and colonization.