Blumeria graminis secretes an extracellular catalase during infection of barley: potential role in suppression of host defence

SUMMARY The obligate biotrophic fungal pathogen of barley, Blumeria graminis f.sp. hordei (Bgh), elicits a burst of H2O2 in its host barley at sites of germ tube invasion. To evaluate whether this specialized pathogen has any antioxidant response to this oxidative burst, the Bgh catB gene was characterized and transcript‐profiled together with other genes implicated in the management of oxidative stress (catalase‐peroxidase, cpx; glutathione peroxidase, gpx; superoxide dismutase, sod1) and in comparison with the constitutively expressed Bghβ‐tubulin and elongation factor1 (ef1) genes. Gel‐based and real‐time RT‐PCR revealed enhanced numbers of catB transcripts at mature primary germ tube and appressorium germ tube (AGT) stages in a susceptible host. Moreover, an anti‐CATB polyclonal antibody, from Aspergillus fumigatus, which recognizes both native and recombinant Bgh CATB, revealed an intense circle of immunofluorescence at the host–pathogen interface at the AGT tip and within the halo area surrounding the host papilla. A new diaminobenzidine‐based ‘scavenger’ assay revealed areas of H2O2 clearing at sites of fungal invasion, provoking speculation that Bgh catalase activity may contribute to pathogenicity in Bgh.