| Genomic comparison of two Xanthomonas campestris pv. campestris (Xcc) strains, Xcc 8004 and Xcc ATCC33913, revealed that the two Xcc strains share 97.5% amino acid homology, whereas they might undergo large genomic reorganization during their evolution. The main discrepancies include: (1) The genome size of Xcc 8004 is 72,538bp larger than that of Xcc 33913; (2) The inverted rearrangement of a large segment and two smaller segments, and a translocated fragment were identified; (3) There are two strain specific genomic islands, designated as giX8-a and giX8-b, respectively in Xcc 8004 and one specific genomic islands in Xcc 33913, named giX3-a; (4) Xcc 8004 is more virulent than Xcc 33913 on a certain cultivar of radish, the Baisha Nanbanzhou.The genomic differences in different geographical isolates were analyzed by using PCR and Southern blotting. The results revealed that all of the Xcc isolates harbor the similar pathogenic clusters, such as gum?hrp?LPS?type II secretory system cluster, same as that in Xcc 8004 and 33913. The patterns of genomic rearrangements found betweengenomes of 8004 and 33913, were not identified in genomes of all Chinese isolates. The strains specific genomic islands giX8-a, giX8-b and giX3-a were found absent in all the genomes of the Chinese, but the three Chinese isolates, No.l, No.3 and No.11 were found containing the giX8-a.The phenotypic analysis showed that the Xcc strains differ significantly in EPS production and pathogenicity. This study demonstrated that the genomic structure in Xcc strains is in its high plasticity during their evolution, but it is conserved in the clusters related to pathogenicity. |
PDF Full Text Request