Eukaryotic translation initiation factor OseIF5A4 negatively regulates rice immunity against blast and bacterial blight diseases

The RING-type E3 ligase OsBBI1 regulates rice resistance against Magnaporthe oryzae through modifying cell wall defenses. In this study, we report the function of an OsBBI1 substrate, eukaryotic translation initiation factor OseIF5A4, in rice immunity. OsBBI1 interacts with OseIF5A4 and other four members of the OseIF5A family. The RING domain in OsBBI1 and the eIF-5a domain in OseIF5A4 are critical for the OsBBI1-OseIF5A4 interaction. OsBBI1 ubiquitinates OseIF5A4 and mediates its degradation in vitro and in vivo . Moreover, the expression of OseIF5A4 was upregulated during early stage of compatible interaction but downregulated in incompatible interaction between rice and M. oryzae . Knockout of OseIF5A4 enhances rice immunity against M. oryzae and Xanthomonas oryzae pv. oryzae , boosts pattern-triggered immune responses, and strengthens pathogen-induced defense responses (e.g., expression of defense genes, accumulation of reactive oxygen species and reinforcement of cell wall). However, overexpression of OseIF5A4 attenuates rice immunity and immune responses. These results demonstrate that OseIF5A4, a substrate of the immunity-associated E3 ligase OsBBI1, negatively regulates rice immunity against M. oryzae and X. oryzae pv. oryzae through modulating pathogen-induced defense responses, highlighting the importance of the protein translational machinery in rice immunity.