Ergosterol biosynthesis: a fungal pathway for life on land?

Sterols, essential lipids of most eukaryotic cells, ensure important structural and signaling functions. The selection pressure which has led to different dominant sterols in the three eukaryotic kingdoms remains unknown. Here we investigated the influence of the progression in the different steps of the ergosterol biosynthetic pathway (EBP) on the yeast resistance to transitions from aqueous to aerial media, typical perturbations of the higher fungi habitats. Five mutants of the EBP (ergΔ), accumulating different sterol intermediates in the EBP, and the WT strain were exposed to drying under atmospheric air or nitrogen and wetting. Results show that the progression in the EBP parallels an increase in the yeast resistance to air-drying with a maximal survival rate for the WT strain. When drying/wetting was performed under nitrogen, yeast survival was higher, particularly for the earlier mutants of the EBP. Thus, ergosterol, through its protective role against mechanical and oxidative st...