Intracellular Reactive Oxygen Species-Aided Localized Cell Death Contributing to Immune Responses Against Wheat Powdery Mildew Pathogen.

Reactive oxygen species (ROS)- and hypersensitive response (HR)-mediated cell death have long been known to play critical roles in plant immunity to pathogens. Wheat powdery mildew caused by f. sp. () is a destructive wheat pathogen. Here, we report a quantitative analysis of the proportion of infected cells with local apoplastic ROS (apoROS) versus intracellular ROS (intraROS) accumulation in various wheat accessions that carry different disease resistance genes ( genes) at a series of time points postinfection. The proportion of apoROS accumulation was 70 to 80% of the infected wheat cells detected in both compatible and incompatible host-pathogen interactions. However, intensive intraROS accumulation followed by localized cell death responses was detected in 11 to 15% of the infected wheat cells, mainly in wheat lines that carried nucleotide-binding leucine-rich repeat genes (e.g., , , , , and ). The lines that carry unconventional R genes, () and (a recessive  gene), showed fewer intraROS responses, whereas 11% of line-infected epidermis cells still showed HR cell death, suggesting that different resistance pathways are activated there. Here, we also demonstrated that ROS could not act as a strong systemic signal for inducing high resistance to in wheat, although it induced the expression of pathogenesis-related genes. These results provide new insights into the contribution of intraROS and localized cell death to immune responses against wheat powdery mildew.