Investigating the effects of temperature on bacterial pathogens of common bean

Thesis

Common bean is a staple crop throughout the World, but production is threatened by a number of pathogens. Two major bacterial pathogens of common bean, Pseudomonas savastanoi pv. phaseolicola (Pspph) and P. syringae pv. syringae (Pss) currently infect bean fields in South-Africa. However, Pss incidence is higher at warmer temperatures whilst Pspph incidence is higher at cooler temperature, suggesting that temperature affects bacterial virulence. We were able to successfully replicate this in vivo in controlled conditions and found that temperature indeed affects Pss and Pspph differentially. Pss is more virulent at 28°C while Pspph is more virulent at 21°C. Interestingly, Pss is also more H2O2 tolerant at 28°C than at 21°C and Pspph is more tolerant at 21°C in vitro. We established a transcriptomic screen to determine which genes may be involved in the three-way interaction between temperature, oxidative stress response and virulence in Pss and Pspph. In doing so, we identified some key candidate genes for future work, including some type 3 secretion system effectors. Furthermore, we generated 24 new genome sequences for Pspph, confirmed that this pathovar is monophyletic, and built a pipeline to determine the canonical set of effectors. Altogether, this thesis paves the way to an improved understanding of the effects of abiotic environmental conditions on bacterial pathogenesis, in particular temperature, an understudied factor in plant pathology.

Authors: Piat, JIO

• DOI: 10.5287/ora-bdmkjoogn
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: Pseudomonas; oxidative stress; temperature; phytopathology; plant pathogen