文摘
BackgroundMany species of bivalves exhibit a unique system of mtDNA transmission named Doubly Uniparental Inheritance (DUI). Under this system, species have two distinct, sex-linked mitochondrial genomes: the M-type mtDNA, which is transmitted by males to male offspring and found in spermatozoa, and the F-type mtDNA, which is transmitted by females to all offspring, and found in all tissues of females and in somatic tissues of males. Bivalves with DUI also have sex-specific mitochondrial ORFan genes, (M-orf in the M mtDNA, F-orf in the F mtDNA), which are open reading frames having no detectable homology and no known function. DUI ORFan proteins have previously been characterized in silico in a taxonomically broad array of bivalves including four mytiloid, one veneroid and one unionoid species. However, the large evolutionary distance among these taxa prevented a meaningful comparison of ORFan properties among these divergent lineages. The present in silico study focuses on a suite of more closely-related Unionoid freshwater mussel species to provide more reliably interpretable information on patterns of conservation and properties of DUI ORFans. Unionoid species typically have separate sexes, but hermaphroditism also occurs, and hermaphroditic species lack the M-type mtDNA and possess a highly mutated version of the F-orf in their maternally transmitted mtDNA (named H-orf in these taxa). In this study, H-orfs and their respective proteins are analysed for the first time.