Identification and Characterization of Novel Candidate Effector Proteins from Magnaporthe oryzae .

The fungal pathogen Magnaporthe oryzae secretes a large number of effector proteins to facilitate infection, most of which are not functionally characterized. We selected potential candidate effector genes from the genome of M. oryzae , field isolate P131, and cloned 69 putative effector genes for functional screening. Utilizing a rice protoplast transient expression system, we identified that four candidate effector genes, GAS1 , BAS2 , MoCEP1 and MoCEP2 induced cell death in rice. In particular, MoCEP2 also induced cell death in Nicotiana benthamiana leaves through Agrobacteria-mediated transient gene expression. We further identified that six candidate effector genes, MoCEP3 to MoCEP8 , suppress flg22-induced ROS burst in N. benthamiana leaves upon transient expression. These effector genes were highly expressed at a different stage after M. oryzae infection. We successfully knocked out five genes in M. oryzae , MoCEP1 , MoCEP2 , MoCEP3 , MoCEP5 and MoCEP7 . The virulence tests suggested that the deletion mutants of MoCEP2 , MoCEP3 and MoCEP5 showed reduced virulence on rice and barley plants. Therefore, those genes play an important role in pathogenicity.