Effect of fenpiclonil on phosphorylation of glucose in Fusarium sulphureum

Abstract

The phenylpyrrole fungicide fenpiclonil inhibited the metabolism of glucose in mycelium of Fusarium sulphureum Schlecht at a concentration which only slightly inhibited mycelial growth (EC,,). At the same concentration, fenpiclonil also inhibited accumulation and, to a greater extent, phosphorylation of 2-deo~y[U-'~C]glucose in starved mycelium loaded with unlabelled 2deoxyglucose. Fenpiclonil did not affect cell-free phosphorylation of 2deoxyglucose or the ATP content of mycelium. Therefore, the primary mode of action of the fungicide may be based on inhibition of transport-associated phosphorylation of glucose. This may cause a cascade of metabolic events which eventually lead to fungal growth inhibition and death. One major event affected by inhibition of transport-associated phosphorylation is the accumulation of polyols, such as glycerol and mannitol, in mycelium. This was not observed in an osmotically sensitive, fenpiclonil-resistant laboratory isolate of the fungus.

Phenylpyrroles: 30 Years, Two Molecules and (Nearly) No Resistance

“…Exposure to high doses of fenpiclonil (over 10-fold EC 50 concentrations) induces the accumulation of amino acids and monosaccharides (Jespers et al, 1993). Conversely the exposure to sub-lethal doses of phenylpyrroles seems to inhibit the incorporation of mono-saccharides into macromolecules (Jespers and De Waard, 1994) but also to stimulate biosynthesis and intracellular accumulation of glycerol and mannitol (Jespers and De Waard, 1995; Pillonel and Meyer, 1997). In order to precise the enzymatic step inhibited by phenylpyrroles, Jespers and De Waard (1995), studied the fate of radioactively labeled 2-deoxyglucose.…”

“…In the presence of fenpiclonil, [ 14 C]-2-deoxyglucose accumulated intracellularly, while the intracellular concentration of [ 14 C]-2-deoxyglucose-phosphate diminished indicating the inhibition of hexokinase activity during exposure of the mycelium to the phenylpyrrole. When the authors performed the same assay on crude mycelial extracts, they only observed a minor reduction of [ 14 C]-2-deoxyglucose phosphorylation under high concentrations of fenpiclonil, withdrawing the cytoplasmic hexokinase as sole or direct target of fenpiclonil (Jespers and De Waard, 1995). …”

Osmoregulation and Fungicide Resistance: the Neurospora crassa os-2 Gene Encodes a HOG1 Mitogen-Activated Protein Kinase Homologue

“…Wild-type N. crassa strains treated with fenpiclonil and fludioxonil at concentrations that inhibited fungal growth by 50% accumulated high concentrations of intracellular glycerol (26). Some Ustilago maydis and F. sulphureum mutants resistant to phenylpyrrole fungicides also were sensitive to high osmotic pressure (13,14). These studies suggested that there is a relationship between osmoregulation and phenylpyrrole fungicide resistance.…”

“…They are broadspectrum fungicides used to control a variety of important plant-pathogenic fungi. Previous studies with Fusarium sulphureum Schlecht indicated that fenpiclonil inhibited the transport of monosaccharides and caused intracellular accumulation of polyols, such as glycerol and mannitol (13,14). Wild-type N. crassa strains treated with fenpiclonil and fludioxonil at concentrations that inhibited fungal growth by 50% accumulated high concentrations of intracellular glycerol (26).…”

Reconstitution and Characterization of Aminopyrrolnitrin Oxygenase, a Rieske N-Oxygenase That Catalyzes Unusual Arylamine Oxidation

“…Biological activity of pyrrolnitrin at low concentrations was demonstrated to be due to the uncoupling of oxidative phosphorylation in Neurospora crassa and at higher concentrations due to inhibition of electron transport both in the flavin region and through cytochrome c oxidase (6). Recently, it was reported that pyrrolnitrin leads to glycerol accumulation and stimulation of triacylglycerol synthesis, resulting in leaky cell membranes and concomitant breakdown of biosynthetic activity followed by cessation of cell growth (7).…”