Molecular Mechanism Of Fungal Growth And Development Regulated By Morak1 In Magnaporthe Oryzae

Magnaporthe oryzae,one of the most devastating causal agents during rice cultivation,causes rice blast disease,which is responsible for annual losses of up to 30% of the worldwide rice harvest.It is well known that maintaining the cell wall integrity as well as fungal spore adhesion is critical for plant infection and disease severity.Therefore,identification of molecular mechanism of M.oryzae development is crucial for rice blast disease control.Receptor for activated C kinase 1（RACK1）protein plays important roles in regulating growth and developmental processes in Fungi.In this study,we characterized a RACK1 protein MGG₀4719 in M.oryzae that is orthologous to Asc1 in Saccharomyces cerevisiae.Sequence analysis revealed that this protein had seven WD40 repeat motifs,which are similar to the motifs in mammalian RACK1,and could partially complement the growth defect of Asc1 mutant of S.cerevisiae.Therefore,MGG₀4719 was designated as Morak1.The Morak1 has localized in the cytoplasm and was highly expressed during conidiation and initially infection.Two gene deletion mutants,designated as Morak1-2 and Morak1-3,were acquired by introducing the gene knock-out vector into M.oryzae according to the principle of homologous recombination.Our results showed that Morak1 deletion caused retarded mycelia growth,and the mutant exhibited increased sensitivity to hydrogen peroxide.The Morak1 exhibited severe defects on conidiation and conidial morphology,but no defects on sexual reproduction.Adhesion assay revealed that Morak1 mutant were defective in fungal adhesion due to the reduced secretion of STM.The mutants are unable to penetrate into epidermic cells or infect the host plants due to the deficiency in cell wall development,which caused the insufficient accumulation of turgor pressure within appressorium and sensivity to cell wall stressor,thereby rendering the mutants attenuated virulence.Taken together,we characterized a RACK1 orthologous MGG₀4719 in M.oryzae,named Morak1.Our study provides new evidence on the conserved function of RACK1 and indicates that Morak1 is involved in vegetative growth,asexual reproduction,conidial morphogenesis,call wall integrity,adhesion and virulence of M.oryzae.