APIP10 Is a Novel E3 Ligase That Functionally Connects the Fungal Effector AvrPiz-t to Its NLR Receptor Piz-t in Rice

In plants, the nucleotide-binding domain, leucine-rich repeat (NLR) family is the major class of intracellular immune receptors that functions in defense against pathogens. Despite extensive research, the mechanism that control NLR activation and immune signaling after the recognition with its cognate avirulence effector has not been fully elucidated. We previously isolated the avirulence effector AvrPiz-t from the fungal pathogen Magnaporthe oryzae and its cognate NLR receptor Piz-t in Oryza sativa (rice). Here, we report that AvrPiz-t targets the rice E3 ligase APIP10 (AvrPiz-t Interacting Proteins 10) for degradation but in return APIP10 ubiquitinates AvrPiz-t that causes its degradation in planta. Silencing of APIP10 in the non-Piz-t background leads to a significant reduction of flg22-induced ROS generation, suppression of defense-related gene expression and enhanced susceptibility against M. oryzae. Interestingly, silencing of APIP10 in the Piz-t background causes severe cell death, significant accumulation of Piz-t and enhanced resistance to M. oryzae, suggesting that APIP10 is a negative regulator of Piz-t.  In addition, we show that APIP10 promotes degradation of Piz-t via the 26S proteasome system. Furthermore, we demonstrate that AvrPi-z-t stabilizes Piz-t during M. oryzae infection. Together our results show that APIP10 is a novel host E3 ligase that functionally connects the fungal effector AvrPiz-t to its NLR receptor Piz-t in rice.