Identification of NoxD/Pro41 as the homologue of the p22phox NADPH oxidase subunit in fungi

Summary NADPH oxidases (Nox) are membrane complexes that produce O2−. Researches in mammals, plants and fungi highlight the involvement of Nox-generated ROS in cell proliferation, differentiation and defense. In mammals, the core enzyme gp91phox/Nox2 is associated with p22phox forming the flavocytochrome b558 ready for activation by a cytosolic complex. Intriguingly, no homologue of the p22phox gene has been found in fungal genomes, questioning how the flavoenzyme forms. Using whole genome sequencing combined with phylogenetic analysis and structural studies, we identify the fungal p22phox homologue as being mutated in the Podospora anserina mutant IDC509. Functional studies show that the fungal p22phox, PaNoxD, acts along PaNox1, but not PaNox2, a second fungal gp91phox homologue. Finally, cytological analysis of functional tagged versions of PaNox1, PaNoxD and PaNoxR shows clear co-localization of PaNoxD and PaNox1 and unravel a dynamic assembly of the complex in the endoplasmic reticulum and in the vacuolar system.