AsianScientist (Jun. 7, 2017) – Researchers at Hong Kong Baptist University (HKBU) and the Hong Kong University of Science and Technology (HKUST) have assembled the 1.64-gigabyte genome of a deep-sea mussel. The mussel genome, published in Nature Ecology & Evolution is the first complete genome of a deep-sea macrobenthic animal and could shed light on symbiosis in other marine organisms such as giant tubeworms and giant clams.
Deep-sea organisms including mussels thrive in the extreme environments of hydrothermal vents and cold seeps which are characterised by high hydrostatic pressure, lack of photosynthesis-derived food, variable temperatures and high concentrations of toxic substances. Despite their ability to survive under stressful conditions, a lack of genomic resources has hindered the understanding of their molecular mechanisms of adaptation.
The research team, led by HKUST’s Professor Qian Pei-Yuan and HKBU’s Associate Professor Qiu Jian-Wen, used a specimen collected in 2013 during Qiu’s participation in China’s manned submersible Jiaolong’s expedition of the South China Sea for the research.
The researchers sequenced the genome of the deep-sea mussel Bathymodiolus platifrons as well as its shallow-water relative Modiolus philippinarum collected from a local softshore in Tingkok for comparison of genomic features.
Through phylogenetic analysis, the research team discovered that modern deep-sea mussels are the descendants of shallow-water mussels, and their ancestors migrated to the deep sea approximately 110 million years ago, providing evidence to support a hypothesis that their ancestors survived through an extinction event during the global anoxia period associated with the Palaeocene-Eocene Thermal Maximum which occurred around 57 million years ago.
Genome comparison revealed that the great expansion of several gene families in the deep-sea mussel may be related to its adaptation to the deep sea. For instance, the expansion of the heat shock protein 70 family, a family of proteins that are produced by a cell in response to exposure to stressful conditions, may help the mussel stabilise protein structures. The expansion of the ABC transporters family, the unit of the transport system, may enhance the mussel’s ability to move toxic chemicals outside its gill epithelial cells.
The expansion of gene families related to immune recognition, endocytosis and caspase-mediated apoptosis indicates the mussel’s adaptation to the presence of chemoautotrophic endosymbionts in its gills. An additional proteomic analysis of the deep-sea mussel gill reveals nutritional and energetic dependency of the mussel on its methanotrophic symbionts.
“The study has provided genomic resources for understanding how the deep-sea mussel has adapted to the abiotic stresses and lack of photosynthesis-derived food in the deep-sea chemosynthetic environment. The general mechanisms of symbiosis revealed in the study are of relevance to other symbiotic organisms such as deep-sea tubeworms and giant clams,” Qian said.
“The genomic resources will facilitate various studies, including genetic connectivity among deep-sea populations, which is relevant to the establishment of deep-sea marine reserves,” Qiu added.
The article can be found at: Sun et al. (2017) Adaptation to Deep-sea Chemosynthetic Environments as Revealed by Mussel Genomes.
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Source: Hong Kong Baptist University.
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