Resumen de Aproximacions en la interacció de ralstonia solanacearum amb solanum dulcamara i solanum tuberosum
Ralstonia solanacearum is one of the most destructive bacterial plant pathogens worldwide. It causes bacterial wilt on more than 200 plant species, among them economically important crops. A big effort has been done during the last decades in order to identify the most relevant virulence factors of this pathogen, but a comprehensive and dynamic understanding of the gene expression profile of these virulence determinants along the infection process was lacking. Also, different groups have identified wild reservoir hosts of R. solanacearum, which has helped in broadening the knowledge of how this bacterium completes its complex life cycle. However, the information regarding the interaction between R. solanacearum and its reservoir hosts was very scarce.
In this thesis, we have tackled the first challenge by establishing three different infection stages of R. solanacearum UY031 strain in potato: apoplast, early xylem and late xylem. The bacterial transcriptome along the infection process and its analysis revealed how R. solanacearum activates or represses specific virulence genes to hijack plant defences as well as the use of bacterial metabolic pathways to facilitate the colonization of different plant tissues during the infection. We underscore the fact that R. solanacearum induces the expression of most of its type III effectors during the xylem phase. In addition to that, different types of motility are regulated and associated to different plant environments and last but not least, that R. solanacearum largely depends on the activation of different nitrogen metabolism genes to adapt to the hypoxic xylem vessels.
The second big challenge of this thesis has been to understand how R. solanacearum interacts with its reservoir host Solanum dulcamara. After analysing the infection process using different inoculation methods, we concluded that S. dulcamara it is not only a reservoir host but also a tolerant host of R. solanacearum, since similar bacterial loads are found compared to other susceptible hosts, but the bacterial wilt symptoms are much lower. We learned that S. dulcamara presents a very stable xylem lignification, which is not impaired upon bacterial infection, partly explaining this tolerant phenotype. Lastly, we found out that S. dulcamara tolerance against R. solanacearum is even more clear at cooler temperatures, underscoring the importance of the environment when investigating plant pathogen interactions.
In summary, this work provides both a solid ground for in planta R. solanacearum functional and characterization studies of different virulence factors, as well as an insight of how the bacterium behaves inside its reservoir tolerant host S. dulcamara.
