Comparative Genomics And Host Specificity Analysis Of Ralstonia Solanacearum Race4Strain SD54

Bacterial wilt caused by Ralstonia solanacearum is one of the most importantand widespread soil-borne disease, and results in serious losses of plant in the world,So far there is no efficient method to control. The host range, pathogenicity andbacteriological characteristics of R. solanacearum strains in different regions ordifferent host plants origin are not exactly the same. With the development ofmolecular biology and DNA sequencing technology, bacterial genomics research hadbeen continuously strengthened, and more and more pathogens were sequenced. Sofar, four out of five different R.solanacearum races had been sequenced or would befinished sequencing, except for race4. Therefore, in order to study the pathogenicspecificity of R. solanacearum race4strain SD54, and to get more information andcorrelation between SD54and its host plant ginger, the whole genome sequencing,comparative genomics and pathogenic specificity analysis of SD54were performed,and the main results are as follows:1. Genome sequencing and comparative genomics analysis of R.solanacearumrace4strain SD54（1）The whole genome of SD54was sequenced by Illumina (Solexa) and454,then through gap finishing, and finally the draft genome of SD54was obtained. Thesize of SD54whole genome is5,784,798bp, the average GC content is67%,encoding5,496CDS,56tRNA and4rRNA (5s-16s-23s).（2）Pan-genome analysis of SD54and other6different R.solanacearum strainsshowed that there were606specific genes in SD54, and these specific genes could beused to study pathogenic specificity and classify different R.solanacearum strains.The construction of phylogenetic tree made the evolution relationships of SD54clearly and also provided the foundation for the future study of R.solanacearum.Collinearity analysis of SD54showed that the bigger collinearity, the more closeevolutionary relationship. Further analysis showed that the SD54genome contained6genomic islands which included a total of63genes, and the average GC content of the6genomic islands is58%. Genomic islands were the results of horizontal genetransfer of exogenous DNA, which maybe make the R.solanacearum more effectivelyinfect host plants and expand its host range. Comparative genomics analysis of SD54 with other six published strains and seven sequenced R.solanacearum strains in thisstudy showed that there existed four specific regions Scaffold32, Scaffold48,Scaffold75and Scaffold76in SD54, and also a specific hrpG gene was found at the5’end of Scaffold76. The hrp genes are necessary for R.solanacearum pathogenicity,indicates that the hrpG gene maybe correlated with the pathogenic specificity ofSD54.2. Mutation of R. solanacearum hrpG gene and its function analysisTo identify the function of hrpG gene in SD54, a suicide vector of hrpG genewas constructed and introduced into the wild-type R. solanacearum SD54throughelectroporation. After homologous recombination, the hrpG mutants were generatedand identified, and the pathogenic test of the hrpG mutants is undergoing.