MoALE1, an ART-like effector, contributes to rice blast virulence through host immune suppression

Abstract

Rice blast, caused by the hemibiotrophic fungus Magnaporthe oryzae, is one of the most destructive diseases affecting rice production worldwide. During infection, M. oryzae secretes effector proteins that suppress host immunity and facilitate colonization. Here, we characterized MoALE1, a predicted effector that is structurally similar to members of the heat-labile enterotoxin/cholera toxin family. Using a yeast secretion trap assay, we demonstrated that MoALE1 contains a functional signal peptide. A MoALE1-GFP fusion localized to the biotrophic interfacial complex, indicating that MoALE1 is a cytoplasmic effector. Expression analyses revealed that MoALE1 is expressed during biotrophy, from 16 to 48 h post-inoculation. Transient expression in Nicotiana benthamiana showed that MoALE1 suppresses BAX-mediated cell death, suggesting a role in host immune suppression. To investigate its contribution to pathogenicity, a{Delta} moale1 mutant was generated and evaluated in rice infection assays. Deletion of MoALE1 significantly reduced disease severity but did not affect fungal growth, stress tolerance, sporulation, appressorium development, host penetration, or early invasive growth. In contrast, infection by the {Delta}moale1 mutant resulted in enhanced host H2O2 accumulation and increased expression of ROS-associated defense genes. Together, these findings identify MoALE1 as a biotrophy-associated cytoplasmic effector that promotes rice blast pathogenicity by suppressing host immune responses and provide new insight into the function of ADP-ribosyltransferase (ART)-like effector candidates in M. oryzae .