Eugenol has antifungal activity and is recognised as having therapeutic potential. However, little is known of the cellular basis of its antifungal activity and a better understanding of eugenol tolerance should lead to better exploitation of eugenol in antifungal therapies. The model yeast, Saccharomyces cerevisiae, expressing apoaequorin was used to show that eugenol induces cytosolic Ca2+ elevations. We investigated the eugenol Ca2+ signature in further detail and show that exponentially growing cells exhibit Ca2+ elevation resulting exclusively from the influx of Ca2+ across the plasma membrane whereas in stationary growth phase cells Ca2+ influx from intracellular and extracellular sources contribute to the eugenol-induced Ca2+ elevation. Ca2+ channel deletion yeast mutants were used to identify the pathways mediating Ca2+ influx; intracellular Ca2+ release was mediated by the vacuolar Ca2+ channel, Yvc1p, whereas the Ca2+ influx across the plasma membrane could be resolved into Cch1p-dependent and Cch1p-independent pathways. We show that the growth of yeast devoid the plasma membrane Ca2+ channel, Cch1p, was hypersensitive to eugenol and that this correlated with reduced Ca2+ elevations. Taken together, these results indicate that a cch1p-mediated Ca2+ influx is part of an intracellular signal which protects against eugenol toxicity. This study provides fresh insight into the mechanisms employed by fungi to tolerate eugenol toxicity which should lead to better exploitation of eugenol in antifungal therapies.
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