| Soil salinization seriously affects the normal growth of plants,endangers the development of China’s ecological environment and agriculture,and seriously results in crop yields.In our laboratory,KLBMP 4941 was discovered on a halophytic plant of Limonium sinensis as an object in the early stage,and it could be promoted through tissue culture.Therefore,this dissertation focuses on how to promote the growth of the host plant under salt stress and the mechanism of interaction between the colonization of the rhizosphere.The pot experiment was conducted to analyze the physiological characteristics and the whole genome of KLBMP 4941.The root exudates were introduced.The study of the interaction between Limonium sinensis and KLBMP 4941,we found some results:1、We used the previously validated endophyte KLBMP 4941 with the best plant growth-promoting,and inoculated KLBMP 4941 with 200 mM NaCl and uninoculated.We study the role of KLBMP 4941 in promoting the growth and related mechanisms of Limonium sinensis.The results showed that under salt stress,the inoculation of Limonium sinensis in the root length,stem length and fresh weight was significantly higher than that of uninfected Limonium sinense.The ion content was determined in the leaves of Limonium sinensis.The concentration of Na~+was lower than that of the control group and increased K~+/Na~+ratio.KLBMP 4941 could promote the content of proline in leaves of plants.Studies on anti-oxidation system showed that there were a certain amount of SOD,CAT and POD in the plants were improved.Therefore,it can be seen that KLBMP 4941 contribute to salt tolerance of host plant.2、In order to continue to analyze the salt-promoting effect of KLBMP 4941,we analyzed its genome.Through the three-generation sequencing of KLBMP 4941,we found that it has a circular chromosome and two plasmids with a total genome size of4,104,242bp and a G+C content of 38.09%.A total of 3426 genes were divided into20 functional categories of orthologous groups(COG),most genes and amino acid transport and metabolism,carbohydrate transport and metabolism,transcription,DNA replication,recombination and repair,and inorganic ion transport,cell motility and metabolism and other functions.For the KLBMP 4941 genomic analysis,genes related to plant growth promoter(PGP),Such as nitrogen fixation,iron carrier biosynthesis,phenazine antibiotic biosynthesis,spermidine and plant volatile biomass3-hydroxy-2-butanone(acetoin)synthesis;The bacteria themselves have a series of genes that are resistant to salt stress,such as Na~+/H~+antiporter,glycine betaine transporter and betaine aldehyde dehydrogenase.Some resistance genes,such as SOD and POD,have also been found;and genes associated with chemotaxis,such as flagellar synthesis,are also found in the genome.Spermidine synthesis-related genes were also found;and genes associated with chemotactic swimming were also found in the genome.Genome analysis showed that the strain KLBMP 4941 has multiple salt-tolerant genes and genes that promote plant growth.3、In this experiment,the persistently expressed green fluorescent of protein(GFP)in plasmid PHT43 was successfully introduced into KLBMP 4941 by protoplast transformation,called 4941-GFP,was successfully obtained.The bacteria can be observed under the fluorescence microscope to emit green fluorescence,but the fluorescence intensity is weak,and the basic fluorescence disappears after passage to the eighth generation.With the extension of time,the colonization density in the rhizosphere decreased,and the colonization density of the colonies in the roots was about 8.92×10~3 on the first day after colonization,and the colony density was3.75×10~3 after the fifth day after colonization.Under the fluorescence microscope,a colony of 4941-GFP was found on the root of,but due to weak luminescence,it was impossible to photograph.4、Through the collection of root exudates of Limonium sinensis under salt stress,the growth and chemotaxis of KLBMP 4941 by root exudates showed that it can significantly promote the growth of the bacteria and have a significant chemotaxis to the bacteria,thus the root system The secretions were analyzed by GC-MS and found that 2-methylbutyric acid,stearic acid,palmitic acid,palmitoleic acid,eugenol and oleic acid were the main components of the root exudates.Purity of KLBMP 4941with a purity of more than 99%monomer compound(concentration of 0.02 g/m L)purchased from Sigma Corporation,change in swimming diameter,capillarity chemotaxis assay,and monomeric compound against KLBMP 4941 under water culture conditions Studies on the effects of rhizosphere colonization density have found that palmitic acid and palmitoleic acid can effectively promote the growth of strains,while eugenol can inhibit their growth.The chemotaxis response of KLBMP4941 to 2-methylbutyric acid,palmitic acid,and palmitoleic acid was stronger,and the chemotaxis reaction to eugenol was weaker.The addition of 2-methylbutyric acid,palmitic acid,and palmitoleic acid showed an increase in rhizosphere colonization density and a larger swimming diameter,but eugenol had no significant effect.The Illumina HiSeq high-throughput sequencing platform was used to sequence the KLBMP 4941 transcriptome.It was found that KLBMP 4941 mainly undergoes ABC transporters,two-component regulatory systems,and chemotaxis-related gene transcriptional regulation under conditions mediated by root exudates.Under salt stress-mediated conditions,transcriptional regulation of genes in nutrient metabolism was found.The mechanism of the interaction between KLBMP 4941 and Limonium sinensis was primarily revealed by the root exudatesIn this paper,the mechanism of the promotion of rhizosphere growth promoting bacteria KLBMP 4941 on the growth of Limonium and the preliminary study of the mechanism of the colonization of the rhizosphere,revealed the ecological significance of the endophyte,in order to follow-up study of the interaction between the promoting bacteria and the host. |
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