Characterization of Ralstonia solanacearum mutants with altered phenotypes on exopolysaccharide production, motility, biofilm formation or Arabidopsis pathogenesis
Date Issued
2008
Date
2008
Author(s)
Huang, Pei-Cheng
Abstract
Ralstonia solanacearum causes a deadly wilting disease on a wide range of crops. To achieve a successful infection, R. solanacearum is well equipped with many pathogenesis machineries, including swimming and twitching motility (MO), biofilm formation (BF), production of exopolysaccharides (EPS) and avoidance or suppression of host defenses. The general objective of this study is to characterize mutants of candidate genes involved in R. solanacearum virulence and fitness. Firstly, a group of transposon (Tn5)-insertional R. solanacearum mutants defective in EPS, MO or BF were characterized. Allelic mutants of these mutants displayed consistent phenotypic changes, confirming that the transposon insertions are responsible for the altered phenotypes. Studies on two novel genes related to BF and MO revealed that RSc0727 is related to BF and twitching motility, and that RSp0199 is related to swimming motility. Further cross-examination of a range of mutants suggested that (1) EPS production is required for BF, but its role in swimming and twitching motility is inconclusive; (2) BF and swimming motility seem to be independent of each other, but twitching motility is important to BF. Secondly, previous systematic screens of Tn5-insertional R. solanacearum mutants led to the identification of two mutants displaying normal pathogenesis on tomato but decreased pathogenesis on Arabidopsis. Allelic mutants exhibited similar in vitro characteristics and differential pathogenesis on tomato and Arabidopsis, verifying the transposon insertions are responsible for the altered phenotypes. Multiplication of these mutants in Nicotiana benthamiana and tomato was not significantly different from that of the wild-type strains. However, the significantly decreased mutants’ colonization in Arabidopsis was found to be correlated with differential pathogenesis on tomato and Arabidopsis. Complementation tests further evidenced RSc1206 is essential for cell membrane/envelope integrity. Results gathered from this study suggested that RSc1206 is required for adaptation of this bacterium in different host environments, and the decreased pathogenesis might be due to the alterations in nutrient utilization, reduced stress tolerance, biofilm formation and swimming motility. On the other hand, the mutant 18A7 displayed mostly normal phenotypes under normal and stress conditions, except for its reduced swimming motility which might be related to the decreased pathogenesis on Arabidopsis. However, whether other factors and how they may contribute to the decreased pathogenesis of 18A7 on Arabidopsis still remains to be determined in the future.
Subjects
Ralstonia
exopolysaccharide
biofilm
motility
host adaptation
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