Comparative and functional genomic analyses of the pathogenicity of phytopathogenXanthomonas campestrispv.campestris

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Abstract
Xanthomonas campestrispathovarcampestris(Xcc) is the causative agent of crucifer black rot disease, which causes severe losses in agricultural yield world-wide. This bacterium is a model organism for studying plant-bacteria interactions. We sequenced the complete genome ofXcc8004 (5,148,708 bp), which is highly conserved relative to that ofXccATCC 33913. Comparative genomics analysis indicated that, in addition to a significant genomic-scale rearrangement cross the replication axis between two IS1478elements, loss and acquisition of blocks of genes, rather than point mutations, constitute the main genetic variation between the twoXccstrains. Screening of a high-density transposon insertional mutant library (16,512 clones) ofXcc8004 against a host plant (Brassica oleraceae) identified 75 nonredundant, single-copy insertions in protein-coding sequences (CDSs) and intergenic regions. In addition to known virulence factors, full virulence was found to require several additional metabolic pathways and regulatory systems, such as fatty acid degradation, type IV secretion system, cell signaling, and amino acids and nucleotide metabolism. Among the identified pathogenicity-related genes, three of unknown function were found inXcc8004-specific chromosomal segments, revealing a direct correlation between genomic dynamics andXccvirulence. The present combination of comparative and functional genomic analyses provides valuable information about the genetic basis ofXccpathogenicity, which may offer novel insight toward the development of efficient methods for prevention of this important plant disease.