| P.fluorescens2P24. a biocontrol agent isolated from suppressive soil of wheat take-all disease, proects plant against soil-borne diseases which was caused by some plant pathogens such as bacterial, fungi. P.fluorescens2P24can produce many secondary metabolites, for example,2,4-diacetyphloroglucinol (2,4-DAPG), siderophore, hydrocyanic acid and ptoteinase and so on.2,4-diacetyphloroglucinol is a kind of polyphenol antibiotic which is broadly spectrum. GacS/GacA two-component system is important to regulate the production of antibiotic, hydrocyanic acid, exoenzyme. PcoI/PcoR quorum-sensing (QS) system take part in the biofilm formation and the colonization ability on wheat rhizosphere. In order to understand the P.fluorescens2P24’s resistant mechanism further, in this study, we used the genetic method to study further on the synthesis of the antibiotic2,4-DAPG and QS system.In the first part, a random mutagenesis with mini Tn5was used in reporter stain PM901, which containing a chromosomal phlA::lacZ transcriptional fusion, to screen regulators for phlA transcriptional. A total about10,000ampicillin/gentamincin resistant insertions were screened. About dozen mutants, significantly changed phlA gene expression, were isolated and purified for further study. The amino acid sequence of the interrupted gene in Aa4-29mutant was highly siminar to rpoZ gene, which encoding omega sunit.Gene evidence indicated that inactivation of rpoZ result in decreaseaed expression of the phlA gene and production of2,4-DAPG. Furhermore, rpoZ was also required for the expression of pcol. In addition, the mutant of rpoZ gene reduced the biolilm formation and impaired the colonization ability on wheat rhizosphere. Compared with2P24, the rpoZ mutant almost completely lost its its capacity to protect the cotton from the damping-off caused by Rhizoctonia solani, indicating that the rpoZ acted as an important regulatory element in the complex network controlling expression of biocontrol traits in P.fluorescens2P24. |
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