E3 Ubiquitin Ligase Subunit MogrrA Regulates Fungal Growth And Development In Magnaporthe Oryzae

Magnaporthe oryzae is one of the most devastating phytopathogens of rice plants worldwide and caused great yield loss, which can feed sixty million people. It is well known that asexual spore formation as well as appressoria differentiation determine the severity of rice blast disease. Therefore, research and analysis of molecular mechanism of conidia development and appressoria differentiation has theoretic and practical significance to the rice blast disease control,and improve the quality of rice as well.F-box proteins play diverse roles in regulating growth and developmental processes in fungi and other eukaryotes. In this study, we characterized a SCF E3 ubiquitin ligase complex F-box protein MogrrA in M. oryzae, a homolog of Grrl in Saccharomyces cerevisiae. Sequence analysis revealed the SCF E3 ubiquitin ligase complex F-box protein possessed typical domains of F-box at the N-terminus（from the 102nd amino acid to 143rd amino acid）, and 10 consecutive LRR domain at the C-terminal from the 193rd amino acid to 497th amino acid. Gene deletion mutants MogrrA-2 and MogrrA-7 were acquired by introducing the gene knock-out vector into M. oryzae according to the principle of homologous recombination. Targeted disruption of MogrrA resulted in various defects in vegetative growth, melanin pigmentation, conidial production and resistant to oxidative stress. Consequently, the MogrrA mutants attenuated the virulence on the host plant. Microscope examination revealed that the inability of conidiophores formation is responsible for total defect of conidia production. Although the MogrrA mutants could develop melanized appressoria from hyphal tips, it was unable to penetrate into plant tissues due to the insufficient accumulation of turgor pressure within appressorium, thereby rendering the mutants attenuated virulence. Chitin is a major component of cell wall. Quantitative real-time PCR revealed the chitin synthase encoding genes significantly decreased expression in MogrrA mutants, and central components in MAP kinase pathways and cAMP signaling pathways, such as Pthll, Macl, Pmkl, Mstll and Mst50, which are responsible for normal appressoria differentiation showed reduced expression in MogrrA mutants.Taken together, we characterized a SCF E3 ubiquitin ligase complex F-box protein MGG₁3065.6, named MogrrA. Our results suggest that MogrrA is a central regulator to control genes involving in vegetative growth, asexual and sexual reproduction, maintaining cell wall integrity, conidiation, differentiation of appressoria, hydrophobicity and full virulence of M. oryzae.