The protein phosphatases MoPtc1 and MoPtc2 are induced during pathogen-host interactions and play synergistic roles in regulating MAPK pathways in Magnaporthe oryzae

Abstract

Reversible protein phosphorylation is essential in cellular signal transduction. The rice blast fungus Magnaporthe oryzae, contains six putative type 2c protein phosphatases namely; MoPtc1, MoPtc2, MoPtc5, MoPtc6, MoPtc7 and MoPtc8 respectively. In this study, we carried out transcription expression analysis and found that MoPtc1, MoPtc2 and MoPtc7 are significantly induced during pathogen-host interactions. Subsequent deletions of MoPtc1 or MoPtc2 not only resulted in increased sensitivity to cell wall stress mediated by Congo red but also increased phosphorylation of Mps1-MAPK. By immunoblot analysis, we found that deletion of both MoPtc1 and MoPtc2 resulted in overstimulation of both the HOG1 and Pmk1 pathways in M. oryzae. We also demonstrate that MoPtc1 is recruited directly to Osm1 by the adaptor protein MoNbp2 to inactivate the Osm1 during hypoosmotic stress unlike in budding yeast. Finally, we show that type 2c protein phosphatases are localized in different cellular compartments in the life cycle of Magnaporthe oryzae. Taken together type 2C protein phosphatases MoPtc1 and MoPtc2 play synergistic roles in regulating MAPK signaling pathways in M. oryzae. This work expands our understanding of the MAPK signaling regulation circuits in M. oryzae and the essential roles of type 2C phosphatases in fine-tuning phosphorylation levels of MAPK during fungal development.