Sensitivity of mitochondrial respiration to different inhibitors in Venturia inaequalis

Abstract

The sensitivity of Venturia inaequalis field isolates to inhibitors of the cytochrome bc1 complex at the Qo site (QoIs) was characterised at the molecular, biochemical and physiological level, and compared to other respiration inhibitors. Comparison of a sensitive and a QoI-resistant isolate revealed very high resistance factors both in mycelium growth and spore germination assays. Cross-resistance was observed among QoIs such as trifloxystrobin, azoxystrobin, famoxadone, strobilurin B and myxothiazol. In the mycelium growth assay, antimycin A, an inhibitor of the cytochrome bc1 complex at the Qi site, was less active against the QoI-resistant than against the sensitive isolate. The mixture of QoIs with salicylhydroxamic acid (SHAM), an inhibitor of the alternative oxidase, exerted synergistic effects in the spore germination but not in the mycelium growth assay. Thus, the cytochrome and the alternative respiration pathways are assumed to play different roles, depending on the developmental stage of the fungus. Induction of alternative oxidase (AOX) by trifloxystrobin was observed in mycelium cells at the molecular level for the sensitive but not the resistant isolate. Following QoI treatment, respiration parameters such as oxygen consumption, ATP level, membrane potential and succinate dehydrogenase activity were only slightly reduced in Qo-resistant mycelium cells, and remained at much higher levels than in sensitive cells. In contrast, no difference was observed between sensitive and resistant isolates when NADH consumption was measured. Comparison of the cytochrome b (cyt b) gene of the sensitive and resistant isolates did not reveal any point mutations as is known to occur in resistant isolates of other plant pathogens. It is assumed that QoI resistance in V inaequalis may be based on a compensation of the energy deficiency following QoI application upstream of the NADH dehydrogenase of the respiratory chain.

Exploring Mechanisms of Resistance to Respiratory Inhibitors in Field Strains of Botrytis cinerea , the Causal Agent of Gray Mold

“…We therefore suggest that target alteration was the only mechanism of resistance operating in our data set. However, these results differ from those of a Japanese survey, which reported the absence of the typical G143A mutation from many StrR isolates collected from strawberries or citrus crops (38), consistent with an unknown mechanism of resistance, as reported for other fungi (22,67,70). Moreover, in our fungicide susceptibility test, strobilurins were a See the structure of the molecules in Fig.…”

At Least Two Origins of Fungicide Resistance in Grapevine Downy Mildew Populations

“…One year later, the development of field-reduced sensitivity to azoxystrobin in populations of the plant pathogen Mycosphaerella fijiensis was first observed (49). As for other single-site inhibitors, the longevity of QoI fungicides was thus quickly challenged in the field, and resistant isolates have been described for numerous plant pathogen species, such as Alternaria solani, Blumeria graminis, Mycosphaerella graminicola, Plasmopara viticola, Podosphaera fusca, Puccinia species, Magnaporthe oryzae, and Venturia inaequalis (5,21,22,30,33,35,38,44,49,50,52,54,56). In most cases, resistance to QoI fungicides is conferred by a point mutation in the mitochondrial cytochrome b gene, giving rise to a substitution from glycine to alanine at position 143 (G143A) of the amino acid sequence (25,29,35).…”

Hydrogen Bonding to the Substrate Is Not Required for Rieske Iron-Sulfur Protein Docking to the Quinol Oxidation Site of Complex III

“…It has reportedly displayed various IC 50 values for submitochondrial particles from different species (30). However, evidence is mounting that some fungal species are intrinsically more resistant (30,31), and field applications of famoxadone for fungal disease control have led to rapid development of resistance that renders the inhibitor ineffective (32)(33)(34). How inhibitors such as famoxadone react to fluidity in its binding environment has not been fully explored experimentally, let alone understood.…”