Function Of Flagellin And Type ? Secretion Systems In Fluorescent Pseudomonas Strains

Fluorescent Pseudomonas strains,as a battery of plant rhizosphere growth-promoting bacteria,play an important role in nutrient transformation,innate immunity,stress resistance,and quality improvement of plants.In recent years,multiple copies of flagellins were found from some fluorescent Pseudomonas strains.And more and more type III secretion systems(T3SS),homologous to the flagellum,were mined from the genomes of fluorescent Pseudomonas.In this study,two typical fluorescent Pseudomonas F113 and 2P24 were employed to determine the functions of multi-copy flagellin and T3SS in bacterial motility,plant growth promotion,and interactions with plant cells.The major findings are as follows,P.kilonensis strain F113 has two copies of flagellin proteins,which were named as Fli C-1 and Fli C-2.The amino acid sequences of the two Fli C proteins have 45.04%identity each other,and their Flg22 peptides have 81.82%identity.Single mutants and a double mutant of fli C-1 and fli C-2 genes were constructed to determine the motility and elicitation of plant immunity.The fli C-1 mutant but not the fli C-2 mutant lost swimming and swarming ability completely.The fli C-1 mutant could not trigger plant immunity while the fli C-2 mutant retained the ability to elicit innate immunity.Both the two conserved Flg22 peptides could trigger plant immunity and inhibit primary root elongation of Arabidopsis thaliana.But Flg22-2 was significantly weaker than Flg22-1 which might lie on the 19^thamino acid in the peptide.P.fluorescens strain 2P24 only has one flagellin protein Fli C-1 which dominates the bacterial motility.Both strains 2P24 and F113 have T3SS homologs.The rsc Q-U mutant of strain 2P24 significantly enhanced swimming and swarming abilities but had no effect on twitching ability and flagella production.Transcriptomic analysis reveals that plant leaves have same differentially expressed genes(DEGs)numbers response to inoculation of 2P24 and the rsc Q-U mutant.But when plant roots were treated with the two strains,root transcriptome had significant difference response to the wild type and T3SS mutant.After cultured for 6 hours,2P24 could induce 270 upregulated genes and 230 downregulated genes.Compared to 2P24 treatment,the number of DEGs induced by 2P24?rsc Q-U was significantly increased:The number of downregulated genes are increased from 230 to 1784,The number of upregulated genes are increased from 270 to 340.Among the DEGs,a total of 85 genes that were upregulated by 2P24 and downregulated after the mutation of T3SS were screened out.q-PCR detection confirmed that at least four genes:JAZ10,ERF109,WRKY40,and CML39 were upregulated by T3SS,which were related to plant growth hormone pathway,growth and development.This indicated that T3SS was probably involved in hormone regulation,growth and development of Arabidopsis root system.