Structure basis of the phytoplasma effector SAP05 recognition specificities to plant Rpn10 in ubiquitin-independent protein degradation

Recent research reported an effector protein SAP05 secreted by phytoplasma could hijack hostage Rpn10 subunit of proteasome and target degradation of GATA or SPL transcription factors (TFs) without ubiquitin. As a result, plant phenotypes will be reprogrammed to a state suitable for phytoplasma amplification and insect vector propagation which present prolonged growth cycles, witches broom-like proliferations of leaves and sterile shoots. We are curious about how could SAP05 target degradation bypassing the ubiquitin pathway and if there is any conserved interaction between different species of SAP05 with AtRpn10. Here, we have determined the crystal structure of the AtRpn10 complex with AY-WB or OY SAP05. Structure alignment revealed similar recognition patterns through sequences of two species SAP05 are poor homologous, which suggested phytoplasma may conduct resemble mode in plant infection. After docking the complex structure to the plant proteasome, we found that SAP05s location is near the ATPase central pore, which may be close enough to submit substrate with no need for ubiquitin in the degradation process.