MoRts1, a regulatory subunit of PP2A, is required for fungal development and pathogenicity of Magnaporthe oryzae

Abstract

Protein phosphatase 2 A (PP2A) is a major heterotrimeric serine/threonine protein phosphatase comprised of three subunits, including structural subunits (A), regulatory subunits (B), and catalytic subunits (C). PP2A has been widely shown to involve in a series of cell signal transduction processes such as cell metabolism, cell cycle regulation, DNA replication, gene transcription and protein translation in yeast and mammalian. However, the roles of PP2A in pathogenic fungi Magnaporthe oryzae still remain unclear. We here found that MoRts1, a gene encoding B regulatory subunit of PP2A homologous to Saccharomyces cerevisiae Rts1, showed up-regulated transcription during conidia and initially infectious stage. Subcellular localization revealed that MoRts1-eGFP was localized to the cytoplasm and septum. Targeted disruption of MoRts1 leads to a reduction of mycelial growth and sporulation, as well as the defects of hydrophobicity, melanin pigmentation and cell wall integrity (CWI). The MoRts1 mutants were less pathogenic to the host plants, compared to the Ku80 strain, and the transcriptional levels of several pathogenicity-related Rho GTPase genes, including MoCdc42, MoRho2, MoRho3, MoRho4, MoRhoX and MoRac1, were significantly decreased in the MoRts1 mutants. Besides, two splicing variants of MoRts1 with unique functions of regulating the growth and pathogenicity were identified, and the B56 domain is vital for determining the sporulation and pathogenicity of M. oryzae. Furthermore, MoRts1 was identified to interact with PP2A catalytic subunit MoPPG1 in vivo in M. oryzae. In summary, our results showed that MoRts1 is an important regulator contributing to the fungal development, and pathogenicity of M. oryzae.