Intracellular reactive oxygen species (intraROS)-aided localized cell death contributing to immune responses against wheat powdery mildew pathogen

Abstract

ABSTRACTReactive 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 byBlumeria graminisf. sp.tritici(Bgt) 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 (R genes), at a series of time points post-infection. The proportion of apoROS accumulation was 70-80% of the infected wheat cells detected in both compatible and incompatible host-pathogen interactions. However, intensive intraROS accumulation followed by localized cell death responses were detected in 11-15% of the infected wheat cells, mainly in wheat lines that carried nucleotide-binding leucine-rich repeat (NLR) R genes (e.g.Pm3F, Pm41, TdPm60, MIIW72, Pm69). The lines that carry unconventional R genes,Pm24(Wheat Tandem Kinase 3) andpm42(a recessive R gene), showed very less intraROS responses, while 11% ofPm24line 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 toBgtin wheat, although it induced the expression of pathogenesis-related (PR)genes. These results provide new insights on the contribution of intraROS and localized cell death to immune responses against wheat powdery mildew.