The Powdery Mildew Effector CSEP0027 Interacts With Barley Catalase to Regulate Host Immunity.

Powdery mildew is one of the most important fungal pathogen diseases. The genome of barley mildew fungus, f. sp. (), encodes a large number of candidate secreted effector proteins (CSEPs). So far, the function and mechanism of most CSEPs remain largely unknown. Here, we identify a effector CSEP0027, a member of family 41, triggering cell death in . CSEP0027 contains a functional signal peptide (SP), verified by yeast secretion assay. We show that CSEP0027 promotes virulence in barley infection using transient gene expression and host-induced gene silencing (HIGS). Barley catalase CAT1 is identified as a CSEP0027 interactor by yeast two-hybrid (Y2H) screening, and the interaction is verified in yeast, in and . The coexpression of CSEP0027 and CAT1 in barley cells results in altered localization of CAT1 from the peroxisome to the nucleus. Barley stripe mosaic virus (BSMV)-silencing and transiently-induced gene silencing (TIGS) assays reveal that CAT1 is required for barley immunity against . We propose that CSEP0027 interacts with barley CAT1 to regulate the host immunity and likely reactive oxygen species (ROS) homeostasis to promote fungal virulence during barley infection.