Ecology and Evolutionary Biology, University of Colorado Boulder, Boulder, USA.
Museum of Natural History, University of Colorado Boulder, Boulder, USA.
Proc Biol Sci. 2024 May;291(2023):20232408. doi: 10.1098/rspb.2023.2408. Epub 2024 May 29.
Photosymbioses between heterotrophic hosts and autotrophic symbionts are evolutionarily prevalent and ecologically significant. However, the molecular mechanisms behind such symbioses remain less elucidated, which hinders our understanding of their origin and adaptive evolution. This study compared gene expression patterns in a photosymbiotic bivalve () and a closely related non-symbiotic species () under different light conditions to detect potential molecular pathways involved in mollusc photosymbiosis. We discovered that the presence of algal symbionts greatly impacted host gene expression in symbiont-containing tissues. We found that the host immune functions were suppressed under normal light compared with those in the dark. In addition, we found that cilia in the symbiont-containing tissues play important roles in symbiont regulation or photoreception. Interestingly, many potential photosymbiosis genes could not be annotated or do not exhibit orthologues in transcriptomes, indicating unique molecular functions in photosymbiotic bivalves. Overall, we found both novel and known molecular mechanisms involved in animal-algal photosymbiosis within bivalves. Given that many of the molecular pathways are shared among distantly related host lineages, such as molluscs and cnidarians, it indicates that parallel and/or convergent evolution is instrumental in shaping host-symbiont interactions and responses in these organisms.
异养宿主和自养共生体之间的共生现象在进化上普遍存在，具有重要的生态学意义。然而，这些共生关系背后的分子机制仍不太清楚，这阻碍了我们对它们的起源和适应性进化的理解。本研究比较了不同光照条件下光合双壳贝类（）与其近缘非共生种（）的基因表达模式，以检测可能涉及软体动物光合共生的分子途径。我们发现，藻类共生体的存在极大地影响了共生体组织中宿主的基因表达。与黑暗条件相比，我们发现正常光照下宿主的免疫功能受到抑制。此外，我们发现共生体组织中的纤毛在共生体的调控或光感受中发挥重要作用。有趣的是，许多潜在的光合共生基因在转录组中无法注释或没有直系同源物，这表明光合双壳贝类中存在独特的分子功能。总的来说，我们在双壳贝类中发现了动物-藻类光合共生所涉及的新的和已知的分子机制。鉴于许多分子途径在亲缘关系较远的宿主谱系（如软体动物和刺胞动物）中都有共享，这表明平行和/或趋同进化在塑造这些生物体内的宿主-共生体相互作用和反应中起着重要作用。
