Abstract
Nitric oxide (NO) is typically produced by most Eukaryotic organisms however the mechanisms underpinning the biosynthesis of NO is only known in animals. Mammals deploy a common pathway for the synthesis of NO involving multiple nitric oxide synthases (NOSs), which are produced under diverse conditions. NO-production forms part of the innate immunity response to bacterial Microbial Associated Molecular Patterns (MAMPs). Previously, we have shown that the fungal plant pathogen Fusarium graminearum rapidly upregulates innate immune response associated genes in response to MAMPs. Here, we report that F. graminearum produces NO in response to bacterial MAMPs and show that in F. graminearum, NO is produced by an FgNCP and an FgCYP located to the endoplasmic reticulum membrane where both proteins are predicted to be N-terminally attached by a transmembrane or embedded hydrophobic alpha helix. Deletion of any of these proteins lowered pathogenicity to wheat and radically reduced NO-production. Knockout of the FgNCP also completely blocked deoxynivalenol synthesis needed for pathogenicity indicating that the FgNCP also delivers electrons to another CYP (TRI4) located at the ER. The FgCYP we found to be involved in NO-productions is the same or similar to proteins involved in Eukaryote sterol synthesis (CYP51) reducing lanosterol on the way to the final main sterols different for different Eukaryotes. Lanosterol enriched membranes are known to be inhibited in endocytosis and we found that the deletion of the FgCYP producing NO also completely stopped endocytosis. We further tested consequences of these indications of more than one function and suggest the CYP-protein is most likely an FgCYPNO,ERG involved in both NO and ergosterol synthesis and the NCP is involved in NO, trichothecene and ergosterol synthesis, an FgNCPNO,TRI,ERG. The two proteins shown here to be responsible for NO production in F. graminearum are both highly conserved in Eukaryotes from amoeba to human and homologues are likely candidates for the production of NO in many other eukaryotes including mammals. In consequence with this, a mouse orthologue to FgNCPNO,TRI,ERG could successfully replace FgNCPNO,TRI,ERG both for its role in NO production and plant pathogenicity. Combined, these results provide compelling evidence that the multiple functions of these conserved proteins can be part of the explanation for the links between chronic inflammation, sterols and blood pressure in human.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
↵* Co-first authors
FgNCPNO,TRI,ERG has orthologues in mammals. We tested if the mouse orthologue could complement the functions of the deleted FgNCPNO,TRI,ERG by expressing the mouse gene behind the native fungal promoter. Nitric oxide formation and pathogenicity was restored pointing to that the the mammalian NCP can also be part of an additional NO forming system in mammals. In addition one of the supplementary data files have been corrected by deleting data not used for this manuscript and an extra supplemental figure showing difference in sexual spore formation for the different mutants have been added. Furthermore text and figures have been modified to accommodate the new experiments.