Mitochondrial alternative oxidase contributes to successful tardigrade anhydrobiosis

Anhydrobiosis can be described as an adaptation to lack of water. This adaptation provides some organisms including tardigrades with a set of capabilities allowing them to survive extreme conditions that even do not exist on Earth. However, the underlying cellular mechanisms are still not explained. Available data assumes important contribution of mitochondrial proteins. Since mitochondrial alternative oxidase (AOX) described as a drought response element has recently been proposed for various invertebrates including tardigrades, we have decided to check if AOX is involved in successful anhydrobiosis of tardigrades. Milnesium inceptum was used as a model for the study. We confirmed functionality of M. inceptum AOX and estimated its activity contribution to anhydrobiosis of different duration. We observed that AOX activity was particularly important for M. inceptum revival after longer-term anhydrobiosis but did not affect rehydration stage. The results may contribute to explanation and then application of anhydrobiosis underlying mechanisms.