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Si us plau utilitzeu sempre aquest identificador per citar o enllaçar aquest document: https://hdl.handle.net/2445/200260
Global evaluation of the fitness and virulence determinants in the phytopathogen Ralstonia solanacearum
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[eng] Losses to plant pathogens pose a major threat to global agriculture and food security worldwide. In the context of globalisation and climate change, the emergence and dispersion of pathogens resistant to conventional management strategies causes destructive outbreaks. One of the most important bacterial phytopathogen is R. solanacearum, the causal agent of the bacterial wilt disease, infecting over 200 plant species. R. solanacearum colonises the vascular system of the plants and blocks the water flow by secreting exopolysaccharides, which causes the wilting symptoms. Moreover, it can persist and easily disperse through contaminated soil and waterways. Many different virulence factors have been studied to date but a comprehensive understanding of the transcriptional regulation during the life cycle of this pathogen is lacking. The huge genetic and phenotypic variability of this traditionally tropical pathogen has led to its spread and establishment in temperate regions. To prevent its dispersal and design efficient management strategies, inexistent to date, a thorough understanding of the pathogen infection and dispersion process is of paramount importance.
In this thesis we set to characterise the transcriptomic landscape of R. solanacearum to unravel novel virulence and fitness determinants deployed by the pathogen throughout its life cycle. In the first two chapters, we studied the gene expression profile of the bacterium during in different stages of plant infection (Chapter 1 or C1) and the environmental soil and water stages (Chapter 2 or C2). Overall, we have identified a dynamic expression profile of different metabolism and virulence genes along the life cycle of the pathogen. Consistent with previous analysis, we identified that the Type III secretion system (T3SS) is also transcriptionally active at late stages of infection but also in water. Interestingly, we identified the alkali pH as a cue triggering T3SS expression in water, which links to the pH alkalinisation along infection inside the plant. Moreover, we validated the expression of different virulence factors in planta such as the flagellar or T4P motility along infection. In soil, we identified the expression of multiple metabolic pathways and stress-related genes that are required for the life of the bacterium in the soil. Among them, we described the induction of genes related to lignin degradation, and alternative metabolic pathways to synthetise carbon molecules related to stress tolerance.
The last two chapters have the objective to characterise and describe specific genes potentially involved in virulence and/or fitness of R. solanacearum. In Chapter 3 (C3), we studied the role of the catalase KatE in detail. We proved its importance for the detoxification of the hydrogen peroxide but discovered that, possibly to redundancy, its mutation has no biological effect on the virulence or the life of the bacterium inside the plant. Finally, in Chapter 4 (C4), we took a different approach studying the secretome of R. solanacearum inside the apoplast and xylem sap of the plant. Many potential proteins related to virulence were discovered but we focused on the description of the S8 serine protease protein family. Preliminary results suggest that highly accumulated S8 proteases might be involved in the life of the bacterium inside the plant.
To sum up, this thesis provides with a solid background to further study and characterise virulence and fitness factors important for the life cycle of the bacterium. Additionally, we started the description and characterisation of different potential virulence factors important for the bacterium. All this information might be of use in the future to have a comprehensive knowledge of the pathogen and to design novel and efficient management and control strategies.
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PEDRO JOVÉ, Roger de. Global evaluation of the fitness and virulence determinants in the phytopathogen Ralstonia solanacearum. [consulta: 26 de novembre de 2025]. [Disponible a: https://hdl.handle.net/2445/200260]