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Plant growth-promoting rhizobacteria (PGPRs) can promote plant growth and suppress soil-borne diseases,so the rational application of PGPR strains is one of the effective and promising approaches to overcome crop soil-borne diseases,reduce agricultural chemical fertilizer and support the agricultural sustainability.Bacillus amyloliquefaciens SQR9 is the PGPR strain isolated from the rhizosphere by our laboratory,it has been applied widely in agricultural practice as the microbial fertilizer.This proposal will focuse on the PGPR strain Bacillus amyloliquefaciens SQR9,our previous researches found that the inter-species quorum-sengsing signal autoinducer-2 (AI-2) was related to the biofilm formation,root coloniazation and cell motility of SQR9.However,its not clear for the molecular regulation mechanism of AI-2 on phenotypes metioned above,and so far,the AI-2 signal pathways in the Gram-positive strains have not been elucidated,which hinder the reasonable use and control of the AI-2 signal molecule.Based on all of the reported AI-2 receptor proteins,i.e.LuxP,LsrB and RbsB are belong to Peripla BP4 protein family,we predicted 4 possible AI-2 receptor protein in the SQR9s genome,and we have identified the AI-2 target genes related to biofilm formation and cell motility through the analysis of the transcriptome data of luxS mutant and wild type of SQR9.Based on the results mentioned above,this research include : (1) To test the predicted AI-2 receptor proteins,and to identify the AI-2 uptake genes and AI-2 receptor proteins through screening the TnYLB-1 transposon mutant library of the strain SQR9 and also using other strategies;(2) To further identify the AI-2 target genes responsible for biofilm formation,root colonization and motility through the ways of comparative (phospho)-proteome and further deep analysis of the transcriptome,and also combining with the phenotypical characteristics,to elucidate the functions of the target genes;(3) To clarify the regulation mechanism of AI-2 and its receptors on target genes through the methods: EMSA,DNase I footprinting and lacZ labeling of AI-2 target genes.This research will find the AI-2 receptors and elucidate the molecular mechanisms of the effects of AI-2 and its receptors on the biofilm formation and root colonization,and also improve our understanding of the AI-2 signal transduction in the Gram-positive bacteria,and will provide the theoretical instructions for improving the in situ root colonization and agricultural application of the strain SQR9 and even other PGPR strains.