Research Progress in Area 3 方向 ( 三 ) 課題進展 151 Abstract Deep-sea cold seeps and hydrothermal vents are populated by high densities of invertebrate animals. The animals host symbiotic bacteria that can provide them with energy and nutrition. This study aims to unravel the enigmatic symbiotic associations in deepsea bivalves, one of the most important groups of invertebrates in chemosynthesis-based ecosystems, with an emphasis on the genomic control of symbiosis establishment and maintenance. They propose to sequence the genomes of the bivalves Acharax sp. and Archivesica marissinica as well as their symbionts collected from a cold seep in the South China Sea through the combination of second- and thirdgeneration sequencing technology with chromosome conformation capture method. They will analyze the genomes with emphases on substrate transfer to the symbionts, as well as the remodeling of the host immune systems to accommodate for presence of the symbionts. Overall, sequencing the genomes of the two hosts in the two ends of the phylogenetic tree of Bivalvia, as well as their symbionts, will allow us to gain insights into the origin and evolution of symbiosis in the deep-sea. Research Activities and Progress • Assembled and analyzed the A. marissinica and its sulfur-oxidizing endosymbiont genomes, and published one paper in Molecular Biology and Evolution; • Analyzed the population connectivity and genetic divergence of a deep-sea limpet Bathyacmaea nipponica, and published one paper in Molecular Biology and Evolution; • Completed the genome assembly of Acharax sp. and its sulfur-oxidizing endosymbiont for downstream data analyses; • Successfully extracted DNA from the dead shells of Archivesica spp., and submitted the samples for high throughout sequencing. Key Findings • We revealed the host–symbiont genomes exhibit both tight metabolic complementarity and distinct signatures of coevolution, which allow A. marissinica to thrive in chemosynthesis-based ecosystems; • We unveiled the intricate interactions amongst local habitats, seafloor topography, and ocean currents may have shaped the migration patterns, historical habitat-linked population divergence, and contemporary gene flow of the deep-sea limpet B. nipponica in the Northwest Pacific. Research Output Publication 13 Trained personnel 11 Press releases 3 Understanding the Genomic Basis of Symbiosis in Two Deep-sea Bivalves Prof. Jianwen Qiu Hong Kong Baptist University Fig 1. Genome landscapes of (A) Archivesica marissinica and (B) its sulfur-oxidizing endosymbiont.
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