Abstract
The plant pathogen 'Candidatus Phytoplasma mali' infects apple trees and is associated with apple proliferation, an important disease in European apple growing regions. 'Ca. P. mali' manipulates its plant host by secreting so called effector proteins. The characterization of these effector proteins and the determination of their in planta targets is important to unravel the molecular mechanisms underlying disease and symptom development. Preliminary results show that a 'Ca. P. mali' effector targets the ubiquitination system of the plant, transcription factors of different classes and other host proteins that are involved in immune response regulation. Furthermore a regional genetic variant of another potential 'Ca. P. mali' effector that functionally differs from the variant of the 'Ca. P. mali' strain AT was found.