Predictive role of mitochondrial genome in the stress resistance of insects and nematodes

Certain insects (e.g., moths and butterflies; order Lepidoptera) and nematodes are considered as excellent experimental models to study the cellular stresssignaling mechanisms since these organisms are far more stress-resistant as compared to mammalian system. Multiple factors have been implicated in thisunusual response, including the oxidative stress response mechanisms. Radiation or chemical-induced mitochondrial oxidative stress occurs throughdamage caused to the components of electron transport chain (ETC) leading to leakage of electrons and generation of superoxide radicals. This may becountered through quick replacement of damaged mitochondrial proteins by upregulated expression. Since the ETC comprises of various proteins codedby mitochondrial DNA, variation in the composition, expressivity and regulation of mitochondrial genome could greatly influence mitochondrial roleunder oxidative stress conditions. Therefore, we carried out in silico analysis of mitochondrial DNA in these organisms and compared it with that of thestress-sensitive humans/mammals. Parameters such as mitochondrial genome organization, codon bias, gene expressivity and GC₃ content were studied.Gene arrangement and Shine-Dalgarno (SD) sequence patterns indicating translational regulation were distinct in insect and nematodes as compared tohumans. A higher codon bias (ENC≫35) and lower GC₃ content (≫0.20) were observed in mitochondrial genes of insect and nematodes as compared tohumans (ENC>42; GC3>0.20), coupled with low codon adaptation index among insects. These features indeed favour higher expressivity ofmitochondrial proteins and might help maintain the mitochondrial physiology under stress conditions. Therefore, our study indicates that mitochondrialgenome organization may influence stress-resistance of insects and nematodes.