Dual regulation of RNase P subunit Rpp30 by an acetyltransferase and E3 ligase in rice immunity

RNase P primarily functions in the 5' maturation of tRNAs. However, several protein subunits of the ribonucleoprotein complex perform non-canonical functions in animals, and recent studies suggest similar functions in plant immunity against viral and fungal pathogens. In rice (Oryza sativa), RNase P subunit 30 (OsRpp30) positively regulates immunity and interacts with the histone deacetylase OsHDT701, a known negative regulator of defense against Magnaporthe oryzae. However, the mechanisms controlling OsRpp30 protein turnover remain unclear. In this study, we identified OsHAG704, a histone acetyltransferase, that acetylates and stabilizes OsRpp30, although OsHAG704-mediated acetylation was not required for OsRpp30 stabilization. Overexpression of OsHAG704 enhanced hydrogen peroxide (H₂O₂) accumulation and conferred increased resistance to M. oryzae. Additionally, we identified OsBPM2, a BTB/POZ-domain containing E3 ubiquitin ligase, which also interacts with OsRpp30 and promotes its stability, leading to similar enhancements in H₂O₂ levels and disease resistance. Although OsHAG704 did not physically interact with OsBPM2, both proteins competitively bound to OsRpp30, resulting in mutual interference between their respective regulatory pathways. Together, our findings identify two distinct positive regulators of OsRpp30 stability and immunity, highlighting a coordinated mechanism involving HAT- and E3 ligase-mediated stabilization in rice defense against M. oryzae.