How much selfishness is contained in fungal mitochondria?

Eukaryotic mitochondria are descended from an alphaproteobacterium, which has radically streamlined its genome since. However, mitochondrial genome size varies strongly between eukaryotic lineages; a fact that is attributable to noncoding DNA and selfish genetic elements. While intron evolution had been previously studied in non-lichenised fungal mitochondria, Pogoda et al. (2019) examined the evolution of mitochondria in lichen mycobionts for the first time in detail. Assessment of the intron content of the cox1 gene revealed that intron number varies widely between lichen genera. The observed variation is comparable to that between major eukaryotic assemblages, such as Opisthokonta and Archaeplastida. Bayesian ancestral state reconstruction indicated that introns were gained mostly in asexual genera and lost in sexually reproducing ones. The authors conclude that mitochondrial intron variability in lichenised fungi is similar to that in non-lichenised fungi.

This study provides evidence that at least some mycobiont mitochondria have lost all their introns through streamlining, while others have high numbers of selfish genetic elements. Although delivering valuable information in the shape of a baseline study, Pogoda et al. (2019) fall short of synthesising their key findings and formulating aims for future research. More appropriate data visualisation and brevity would have benefited the reader’s understanding.

Pogoda, C. S., Keepers, K. G., Nadiadi, A. Y., Bailey, D. W., Lendemer, J. C., Tripp, E. A., & Kane, N. C. (2019). Genome streamlining via complete loss of introns has occurred multiple times in lichenized fungal mitochondria. Ecology and Evolution, 9(7), 4245-4263.