Abstract
SAP11 CaPM is the only bacterial effector known to date to be identified as secreted by the apple proliferation phytoplasma. In Malus spp. this effector binds and deactivates two transcription factors of the TCP family, subgroup CIN-class 2. To elucidate the role of SAP11 CaPM and its targets in the context of resistance against apple proliferation phytoplasma (AP), the sequences of the target genes from susceptible and resistant Malus have been compared. Interestingly, some mutations exclusively present in AP resistant Malus x domestica TCP 25 (MdTCP25) could be observed. The MdTCP25 sequences of many other AP-resistant plants were sequenced and a good degree of correlation was found between resistance and presence of the previously detected resistant exclusive mutations. Using a yeast two hybrid-based reporter gene assay, the interaction strength between SAP11 CaPM and MdTCP25 from resistant plants was evaluated. However, no visible differences in interaction strengths between SAP11 CaPM and MdTCP25 from susceptible or resistant Malus could be observed.