Genome Sequence and Characterization of Wheat-Isolated Pseudomonas syringae Strains with a Small Repertoire of Type III Effectors

The gram-negative gamma-proteobacterium Pseudomonas syringae is one of the most wide-spread plant pathogens: different pathovars infect more than 200 host species ranging from grassy to woody plants. These include agriculturally important crops, such as bean, tomato, cucumber, as well as kiwi, stone fruit, and olive trees. As expected from such a wide host range, there also exists a relatively large genetic heterogeneity among different pathovars. This highest degree of variation is found in the composition of virulence factors: even withing the same pathovar different strains deploy different sets of type III effectors (T3Es), as well as phytotoxins and other secreted molecules. Syringolin is a proteasome inhibitor produced by some strains of pathovar syringae. Since up to know it was not possible to establish an infection model for syringolin in Arabidopsis, we decided to explore another common laboratory model plant, wheat (Triticum aestivum), for which we have both a producer strain as well as a strain naturally lacking the toxin. Sequencing of the two genomes and subsequent analysis has placed the two strains into a group within the pathovar syringae which possess a small number of T3Es, suggesting importance of non-type III secreted virulence factors.

The aim of this project is to gain insights into basic virulence mechanisms of P. syringae in a context of only several T3Es. This is addressed by generating mutants of the identified T3Es, toxins, and other potential virulence-associated genes and testing for an influence on endophytic growth and disease development. Results will be reported herein.