Gymnosporangium yamadae Effector GyHRb12 Targets the Host Ribosomal Protein MdRPS20 to Enhance Translation and Suppress Immunity of Apple Leaves

The apple rust fungus Gymnosporangium yamadae (G. yamadae) secretes effector proteins into host apple leaf cells to facilitate parasitism. Among these, the candidate effector GyHRb12 was found to localize to the nucleus upon transient expression in Nicotiana benthamiana leaf cells, although its functional role remained unclear. Subsequent investigations demonstrated that overexpression of GyHRb12 protein decreases plant cell resistance and attenuates the transcription of multiple antifungal-related genes. Using a yeast two-hybrid screen, MdRPS20, a component of the 30S ribosomal subunit, was identified as an interactor of GyHRb12. Proteomic analysis revealed that GyHRb12 modulates the expression of proteins involved in protein translation processes, which may be mediated by changes in ribosomal abundance. Notably, mutating the 14th amino acid in MdRPS20 disrupted its interaction with GyHRb12, underscoring the critical role of this residue in effector recognition and subsequent suppression of host immunity. Collectively, these findings demonstrate that G. yamadae employs a nuclear-localized effector to target a ribosomal subunit protein, thereby reprogramming host translation activity and suppressing host immunity.