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Fusarium oxysporum is a filamentous fungus that is known to invade over a hundred different hosts and poses a major threat to the economy and food supply world-wide. Poly (Adenosine diphosphate-Ribose) Polymerase (PARP) is a family of regulatory proteins that affect change in the cell through transfer of ADP-Ribose moieties onto target molecules. The most well-studied PARP protein is the human PARP1, a PARylating nuclear protein that serves as our model PARP protein. F. oxysporum was found to contain a large expansion of PARP catalytic-domain-containing proteins compared to other filamentous fungi. We utilized in silico multiple sequence alignments and domain predictions to identify a human PARP1 homolog termed foPARP1 that was conserved within the core chromosomes in all three strains within our comparative system. Our in silico predictions also stated that only one strain, an Arabidopsis pathogen, Fo5176, contained several other predicted catalytically active PARP homologs within the accessory chromosome. To test the effect that foPARP1 knockout would have on DNA damage tolerance, we created a foParp1 knockout and found that only strains Fol4287 and Fo5176 had a significant reduction in tolerance upon being plated with methyl methanesulfonate (MMS), a DNA alkylating agent. To test how global PARylation trends would be affected by foParp1 knockout, we utilized immunodot-blotting with PAR antibodies to assess PARylation in total protein extracts. We found that all strains of the comparative system had the capacity to catalyze the synthesis of long PAR chains, while only Fo47 and Fo5176 had a significant PARylation increase when exposed to MMS, and no samples had a significant increase in PARylation within the foParp1 knockouts. Finally, we utilized RNA-Sequencing to determine the transcriptional impacts that foParp1 knockout would have and found aberrant DNA repair pathways and disruptions in stress responses. Taken together, we conclude that foPARP1 is in fact a functional PARP1 homolog and exhibits similar post-transcriptional modification and transcriptional impacts as its human counterpart. However, we were not able to correlate PARP copy number with DNA stress tolerance, and further research would be needed to assess the full function of the PARP expansion.

Fusarium head blight is a devastating fungal disease of cereals caused by the pathogen Fusarium graminearum that leads to important economic losses due to diminished yields and grain downgrading. F. graminearum deploys several secondary metabolites known as virulence factors to facilitate its invasion of host tissues. These include the gramillins, a group of bicyclic lipopeptide ionophores that cause cell death and increased virulence in Arabidopsis, maize, and barley, but not wheat. Ionophores are involved in many plant-microbe interactions, but current knowledge of the molecular mechanisms governing host response to these molecules is limited. Susceptibility to gramillin varies among cultivars of affected species, but the basis for insensitivity has not yet been described, nor has the function of gramillin during infection. Here, we establish ion leakage as a method to survey Canadian barley for sensitivity, demonstrate that insensitivity to gramillin is likely mediated by a plant protease rather than inducible immune responses, and suggest a possible function of gramillin in positively regulating the expression of other fungal virulence factors during infection. This contributes to deepening our understanding of cyclic lipopeptide ionophores and their role during plant-microbe interactions.

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