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SB

Stefano Bettinazzi

METABOLIC REMODELING ASSOCIATED WITH mtDNA: INSIGHTS INTO THE ADAPTIVE VALUE OF DOUBLY UNIPARENTAL INHERITANCE OF MITOCHONDRIA

Stefano Bettinazzi, Enrique Rodriguez, Liliana Milani, Pierre U. Blier, and Sophie Breton

Mitochondria produce energy through oxidative phosphorylation (OXPHOS), which depends on the expression of both nuclear and mitochondrial DNA (mtDNA). In animals, a striking exception from strictly maternal inheritance (SMI) of mitochondria is the doubly uniparental inheritance (DUI). This unique system is found in bivalves and is characterized by the presence of sex-linked mtDNAs (F- and M-type) associated with gametes, and occasionally coexisting in somatic tissues. Considering the adaptive value of mtDNA variations, the high divergence between the two DUI haplotypes (8-40% of DNA divergence) should have a strong phenotypic effect, and their coexistence in somatic tissues could be deleterious. However, whether differences in mitochondrial metabolism underlie this condition is not known. To address this issue, we characterized the OXPHOS activity of oocytes, spermatozoa, and gills, of different bivalve species (DUI and SMI) through high resolution respirometry. Contrary to SMI species, DUI species express different gender-linked mitochondrial phenotypes in gametes and partly in somatic tissues. This metabolic remodeling highlights the adaptive value of mtDNA variations and we propose that bearing specific sex-linked mitochondria could assure the energetic requirements of different gametes. To our knowledge, this is the first example of a phenotype resulting from direct selection for male functions on sperm mitochondria. The absence of interspecific divergence suggests that this mitochondrial reorganization could be a conserved character of DUI, potentially linking male-energetic adaptation, mitotype preservation and inheritance. Specific OXPHOS features are also consistent with resistance to both heteroplasmy and ageing.