2026-04-25 東京大学
ヒメシャコガイの養殖の様子。色鮮やかな外套膜を広げ、内部に共生する褐虫藻に光を当てている。
＜関連情報＞
- https://www.aori.u-tokyo.ac.jp/research/news/2026/20260425.html
- https://www.cell.com/current-biology/fulltext/S0960-9822(26)00395-7
巨大シャコガイの光合成共生に関するゲノム解析とサンゴの戦略との比較 Genomic insights into photosymbiosis in giant clams and comparisons with coral strategies
Taiga Uchida ∙ Hiroshi Yamashita ∙ Go Shimada ∙ Mayumi Kawamitsu ∙ Eiichi Shoguchi ∙ Chuya Shinzato
Current Biology Published:April 24, 2026
DOI:https://doi.org/10.1016/j.cub.2026.03.075
Highlights
- A high-quality genome assembly was obtained for the photosymbiotic giant clam
- Transcriptomic analysis identifies possible symbiosis-related genes in the clam
- NPC2 expression suggests convergent sterol transport in clam and coral symbiosis
- Newly identified animal NRT2 may supply nitrate to symbionts, unlike in corals
Summary
Giant clams are representative bivalves in coral reef ecosystems that host photosynthetic dinoflagellates extracellularly and rely on their photosynthates, functioning as “solar-powered animals.” Unlike corals, which harbor intracellular dinoflagellates, the molecular mechanisms and evolutionary history underlying this symbiosis remain largely unknown. In the present study, we integrated chromosome-scale genome assembly, transcriptome profiling, and bleaching experiments involving giant clams, Tridacna crocea, to explore the genetic basis of extracellular symbiosis. Signals associated with sterol transport by Niemann-Pick type C2 (NPC2) proteins and carbon-concentrating mechanisms suggest that giant clams share some nutrient exchange strategies with corals. Strikingly, the nitrate transporter NRT2, a “plant-like” gene previously thought to be absent in animals, represents an unexpected evolutionary retention that enables nitrate-based nutrient supply, highlighting a fundamental difference from coral symbiosis. Our findings reveal both conserved and distinct molecular strategies of photosymbiosis in reef-dwelling marine invertebrates and provide insights into evolution and ecological resilience of coral reef ecosystems.
