Phytoplasmas are intracellular bacterial plant pathogens that cause devastating diseases in crops and ornamental plants through the secretion of effector proteins. One of these effector proteins, termed SAP54, leads to the degradation of a specific subset of floral homeotic proteins of the MIKC-type MADS-domain family via the ubiquitin-proteasome pathway. Aurin et al. report that, based on biophysical and molecular biological analyses, SAP54 folds into an alpha-helical structure.