MoRpa12, an unconventional secreted effector targets host nuclei, is critical for development and plant invasion of Magnaporthe oryzae

RNA polymerase I (Pol I) is a multi-subunit protein complex that is associated with the transcription of most ribosomal RNA molecules in all eukaryotes. Rpa12 is a small subunit of the catalytic core of Pol I and plays a critical role in RNA cleavage, transcription initiation, and elongation during proliferation in yeast and mammals. However, the function of Rpa12 in phytopathogenic fungi remain uncharacterized. Here, we present the functional characterization of MoRpa12, a homologue of yeast Rpa12, in Magnaporthe oryzae. MoRpa12 shows upregulation during the infectious stage, and the MoRpa12-GFP exhibits nuclear localization at various developmental stages in M. oryzae, and translocates into the nuclei of plant cells after penetration. The MoRpa12 mutants also exhibit substantial defects on mitosis, autophagy, oxidative stress tolerance, cell wall integrity, septin ring assembly, lipid and glycogen metabolism, and pathogenicity. The four cysteine residues at the amino terminus of this protein are critical for the nuclear localization of MoRpa12, and site-directed mutagenesis of them affects localization, fungal penetration, and full virulence of M. oryzae. In conclusion, our findings indicate that MoRpa12 function as an unconventional secreted effector targets host nuclei, and is essential for the growth and plant infection of M. oryzae.