Publications - Faculty - Recently Submitted Faculty Publications 2008
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Wang - Applied and Environmental Microbiology
The galU gene is essential for survival of Xanthomonas axonopodis pv. citri in planta
Yinping Guo, Uma Shankar Sagaram, Jeong-soon Kim, and Nian Wang
Abstract: Xanthomonas axonopodis pv. citri (Xac) is the causal agent of citrus canker. In this study, two non-mucoid mutants of Xac (F6 and D12), were identified in a Xac EZ-Tn5 <R6Kγori/KAN-2>Tnp transposon library. Rescue cloning and sequence analysis indicated that both mutants had transposon insertion in the galU gene. Southern blot analysis showed that one single copy of EZ-Tn5 transposon inserted into the gene galU on Xac chromosome for both mutants. Further study showed that the galU gene was responsible for biosynthesis of extracellular polysaccharides (EPS), capsular polysaccharide (CPS) and lipopolysaccharides (LPS) as well as biofilm formation. Mutation of the galU gene caused loss of pathogenicity on grapefruit. The loss of pathogenicity resulted from the reduced growth of the galU mutant in planta. Although D12 showed similar growth rate as the wild type strain 306 in nutrient broth medium, its population failed to establish in planta or on leaf surface. Co-inoculation of galU mutant with wild type strain did not promote the growth of galU mutant in planta. Defects of EPS production, mucoid phenotype, pathogenicity, and growth in planta of the galU mutant were complemented to wild phenotype using plasmid pCGU2.1 containing an intact galU. These data indicated that galU gene contributes to Xac survival the intercellular spaces and on leaf surface by affecting LPS, EPS, and CPS synthesis as well as biofilm formation.
