Exp5, a Magnaporthe oryzae nucleo-cytoplasmic receptor involved in plant pathogenesis
Karyopherins are involved in the translocation of proteins and/or RNAs between the nucleus and the cytoplasm. The Magnaporthe oryzae karyopherin Exp5 protein is the orthologue of the human karyopherin exportin-5 and the Saccharomyces cerevisiae Msn5. The M. oryzae Δexp5 mutant is strongly impaired in plant disease symptoms production. Therefore, to understand the role of this karyopherin during plant infection we studied Exp5 RNA and protein cargoes. Several t-RNA synthetases, seven subunits of the 26S proteasome and key components of pathogenesis-related signal transduction pathways (MAPKs Pmk1 and Mps1) and fungal metabolism (Tps1) were found to immunoprecipitate with Exp5. An important set of mitochondrial proteins including TIM44 and TOM70 also interacted with Exp5, which suggest that mitochondrial dysfunction can be contributing to the strong root infection defects exhibited by Δexp5. Additional deficiencies such as accumulation of small RNAs derived from transposon elements and tRNAMet in the mutant supports the involvement of Exp5 in ncRNA metabolism and tRNA transport. Overall, our results suggest that Exp5 is required for the transport of specific classes of proteins and ncRNAs, several of which contribute to M. oryzae pathogenicicity.