Mitochondrial alternative oxidase is determinant for growth and sporulation in the early diverging fungus Blastocladiella emersonii.

Blastocladiella emersonii is an early diverging fungus of the phylum Blastocladiomycota. During the life cycle of the fungus, mitochondrial morphology changes significantly, from a fragmented form in sessile vegetative cells to a fused network in motile zoospores. In this study, we visualize these morphological changes using a mitochondrial fluorescent probe and show that the respiratory capacity in zoospores is much higher than in vegetative cells, suggesting that mitochondrial morphology could be related to the differences in oxygen consumption. While studying the respiratory chain of the fungus, we observed an antimycin A and cyanide-insensitive, salicylhydroxamic (SHAM)-sensitive respiratory activity, indicative of a mitochondrial alternative oxidase (AOX) activity. The presence of AOX was confirmed by the finding of a B. emersonii cDNA encoding a putative AOX, and by detection of AOX protein in immunoblots. Inhibition of AOX activity by SHAM was found to significantly alter the capacity of the fungus to grow and sporulate, indicating that AOX participates in life cycle control in B. emersonii.