AbstractThe plant pathogen ‘Candidatus Phytoplasma mali’ (‘Ca. P. mali’) is the causing agent of apple proliferation that leads to heavy damage in apple production all over Europe. To identify and analyze effector proteins of plant pathogens is an important strategy in plant disease research. Here, we report that the SAP11-like protein of ‘Ca. P. mali’ induces crinkled leaves and siliques and witches’ broom symptoms in transgenic Arabidopsis thaliana (A. thaliana) plants and binds to 6 members of class I and all members of class II TCP (TEOSINE BRANCHES/ CYCLOIDEA/PROLIFERATING CELL FACTOR) transcription factors of A. thaliana in yeast two-hybrid assays. Moreover, we demonstrate that the protein localizes actively into the plant nucleus without requiring the nuclear leader sequence (NLS). We also identified a 17 amino acid stretch previously predicted to be a nuclear leader sequence that is important for the binding of some of the TCPs and also responsible for the crinkled leaf and silique phenotype in transgenic A. thaliana.