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<bold>Abstract</bold> Mitochondrial tRNA gene loss and cytosolic tRNA import to mitochondria are two common phenomena in mitochondrial biology, but their importance is often under-appreciated in animals. This is because most bilaterally symmetrical animals (Bilateria) encode a complete set of tRNAs needed for mitochondrial translation. By contrast, studies of mitochondrial genomes in non-bilaterian animals have shown a reduced tRNA gene content in several lineages, necessitating tRNA import. Interestingly, in most of these lineages tRNA gene content appears to be set early in the evolution of the group and conserved thereafter. Here we demonstrate that Clade B of Haplosclerid Sponges (CBHS) represent an exception to this pattern. We determined mt-genome sequences for eight species from this group and analyzed them with six that had been previously available. In addition, we determined mt-genome sequences for two species of haploslerid sponges outside the CBHS and used them with eight previously available sequences as outgroups. We found that tRNA gene content varied widely among CBHS species: from three in an undescribedHaliclonaspecies (Haliclona sp. TLT785) to 25 inXestospongia mutaandX. testudinaria. Furthermore, we found that all CBHS species outside the genusXestospongialackedatp9, while some also lackedatp8. Analysis of nuclear sequences fromNiphates digitalisrevealed that bothatp8andatp9had transferred to the nuclear genome, while the absence of mt-tRNA genes represented their genuine loss. Overall, CBHS can be a useful animal system to study mt-tRNA genes loss, mitochondrial import of cytosolic tRNA, and the impact of both of these processes on mitochondrial evolution. Significance statementIt is generally believed that the gene content is stable in animal mitochondrial (mt) DNA. Indeed, mtDNA in most bilaterally symmetrical animals encompasses a conserved set of 37 genes coding for 13 proteins, two rRNAs and 22 tRNAs. By contrast, mtDNA in non-bilaterian animals shows more variation in mt gene content, in particular in the number of tRNA genes. However, most of this variation occurs between major non-bilaterian lineages. Here we demonstrate that a group of demosponges called Clade B of Haplosclerid Sponges (CBHS) represents a fascinating exception to this pattern, with species experiencing recurrent losses of up to 22 mt-tRNA genes. We argue that this group constitutes a promising system to investigate the effects of tRNA gene loss on evolution of mt-genomes as well as mitochondrial tRNA import machinery.
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This content will become publicly available on February 1, 2027
Organellar genomes of the putative Hawaiian endemic species Gibsmithia punonomaewa (Gigartinales, Rhodophyta): First available genomes for the Dumontiaceae
Abstract We have reported the first mitochondrial (GenBank accession PV035080) and chloroplast (GenBank accession PV035081) genomes for a representative of the gigartinalean family Dumontiaceae (Gibsmithia punonomaewa). High‐throughput sequencing yielded both organellar genomes for the holotype specimen ofGibsmithia punonomaewa, a recently described species that is also a putative endemic to the mesophotic zone of the Hawaiian Islands. Gene content and order of the 26,428‐bp mitochondrial genome are conserved relative to other available genomes of the Gigartinales. The genome contains 52 genes, including 25 protein‐coding sequences (CDSs), 3 rRNAs, and 24 tRNAs, as well as one group II intron in atrnI‐GAU tRNA. The chloroplast genome is 185,316 bp in length and contains 236 genes, including 203 CDSs, three rRNAs, and 30 tRNAs, and one group II intron in atrnM‐CAU tRNA. Both organellar genomes displayed high synteny compared to close relatives in the order Gigartinales, with unique features restricted to several open reading frames. Phylogenomic analyses of the mitochondrial and chloroplast genomes with other gigartinalean representatives yielded well‐resolved phylogenies that supported an early diverging position of the Dumontiaceae within the order Gigartinales.
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- Award ID(s):
- 2242142
- PAR ID:
- 10678068
- Publisher / Repository:
- Phycological Society of America
- Date Published:
- Journal Name:
- Journal of Phycology
- Volume:
- 62
- Issue:
- 1
- ISSN:
- 0022-3646
- Page Range / eLocation ID:
- 9 to 16
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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