Professor Dr Ulla Bonas

Main research interests: plant pathogens, Xanthomonas campestris pv. vesicatoria, defense mechanisms in plants, Bacterial Spot Disease, type III effectors, avirulence genes
Ulla Bonas’ research focuses on the interaction between pathogenic bacteria and plants. She studies the molecular mechanisms of the disease germ Xanthomonas and the plant’s reaction after infection with the germ. Her works significantly contributed to the understanding of plant–microbe interactions and allowed for novel therapy and plant protection concepts.
The bacterial germ Xanthomonas campestris pv. vesicatoria (Xcv) mainly infects crop plants such as bell pepper and tomatoes. Xcv causes the Bacterial Spot Disease, leading to heavy crop losses. To infect the host plant, the bacteria applies sophisticated strategies. By a protein complex (type III secretion system, T3S system), it introduces effector proteins into the plant cell. These effector proteins manipulate the plant’s genes. Cell signaling and metabolism are impaired for the benefit of the germ, and the plant’s defense is suppressed.
Ulla Bonas studies the mechanisms of information transfer between plants and pathogens during recognition phase, virulence (degree of pathogenic properties) and defense. She wants to learn how the germ succeeds in shutting down the plant’s defense and propagating in the plant tissue.
In her research, she unveiled how the bacteria are incapacitated in resistant plants. In various host plants, Xanthomonas causes no disease symptoms, but leads to a programmed cell death within the infected plant tissue (local necrosis). Thus, a further propagation of the germ in the plant is prevented.
However, necrosis is only initiated if avirulent genes of the bacteria and a matching resistance gene (R-gene) are present in the plant. Ulla Bonas and her team have cloned and characterized one of the first avirulence genes (avrBs3-gene) and elucidated its function. Moreover, they isolated the resistance gene corresponding to AvrBs3 in resistant bell pepper plants, i.e., the Bs3-gene. AvrBs3 binds to certain DNA-sequences in genetic switches of Bs3, thus triggering the plant’s defense reaction, i.e., cell death.
During their researches, the scientists discovered a novel and modularly built protein area in AvrBs3, which is able to bind specific locations of genetic material.