Abstract
Among the brown algal lineages, Ectocarpales species have isogamous fertilization in which male and female gametes are morphologically similar. In contrast, female gametes are much larger than male gametes in the oogamous species found in many other brown algal lineages. It has been reported that the plastids of isogamous species are biparentally inherited whereas the plastids of oogamous species are maternally inherited. In contrast, in both isogamous and oogamous species, the mitochondria are usually inherited maternally. To investigate whether there is any relationship between the modes of inheritance and organellar genome architecture, we sequenced six plastid genomes (ptDNA) and two mitochondrial genomes (mtDNA) of isogamous species from the Ectocarpales and compared them with previously sequenced organellar genomes. We found that the biparentally inherited ptDNAs of isogamous species presented distinctive structural rearrangements whereas maternally inherited ptDNAs of oogamous species showed no rearrangements. Our analysis permits the hypothesis that structural rearrangements in ptDNAs may be a consequence of the mode of inheritance.
Highlights
Www.nature.com/scientificreports slightly larger female gametes of Ectocarpus species[7] and near-isogamy in Scytosiphon species[8]
In isogamous Ectocarpales species, mitochondria are commonly maternally inherited but unusual patterns of mitochondrial inheritance such as paternal inheritance or random paternal or maternal inheritance have been described for some strains of Ectocarpus[23]
There were some differences in both size and content between the ptDNAs of the Ectocarpus species-7 strain Ec32 (NC_013498.1; note that Ec32 was originally defined as Ectocarpus siliculosus but has recently been shown to correspond to another species, designated Ectocarpus species-726) and the E. siliculosus strain Ec08
Summary
Www.nature.com/scientificreports slightly larger female gametes of Ectocarpus species[7] and near-isogamy in Scytosiphon species[8]. Analysis of cross-species hybrids confirmed that only mitochondria and plastids from the female gamete are transferred to the zygote during fertilization for both the Laminariales and the Fucales[15,16] These results indicate that organelles are maternally inherited in the oogamous brown algae. In isogamous Ectocarpales species, mitochondria are commonly maternally inherited (demonstrated for Ectocarpus siliculosus and Scytosiphon lomentaria Lyngbye20–22) but unusual patterns of mitochondrial inheritance such as paternal inheritance or random paternal or maternal inheritance have been described for some strains of Ectocarpus[23] Taken together, these observations suggest that the type of fertilization (i.e., isogamy or oogamy) may influence the mode of organelle inheritance. More ptDNA sequence data are needed for the Ectocarpales species to study the evolution of ptDNA in relation to inheritance mode
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