Abbott Evelyn, Dixon Groves, Matz Mikhail
Department of Integrative Biology, University of Texas at Austin, Austin, Texas, USA.
Mol Ecol. 2021 Dec;30(24):6585-6595. doi: 10.1111/mec.16190. Epub 2021 Oct 5.
As sea surface temperatures increase, many coral species that used to harbour symbionts of the genus Cladocopium have become colonized with the thermally tolerant genus, Durusdinium. Here, we asked how gene expression in the symbionts of one genus changes depending on the abundance of another symbiont genus within the same coral host, and what effect this interaction has on the host. Symbiont gene expression was overwhelmingly driven by whether the genus was the minority or the majority within the host, which affected 79% (Durusdinium) and 96% (Cladocopium) of all genes. Particularly strong effects in both genera were observed for photosynthesis components (upregulated in the minority state) and proteins putatively associated with cell motility (upregulated in the majority state). Importantly, there was no distinct gene expression signature associated with the mixed symbiosis state when both genera were represented in comparable proportions within the host, which could lead to more intense competition. The mixed symbiosis was also not associated with elevated host stress: in fact, after heat treatment, stress signatures were the lowest in mixed-symbiosis corals compared to both Cladocopium- and Durusdinium-dominated corals. In conclusion, during shuffling between Cladocopium and Durusdinium both symbiont genera go through extensive and largely reciprocal physiological transitions, but there is no evidence of intensifying antagonistic interactions that are detrimental to the host. Unless the mixed-symbiosis corals in this study are not representative of the typical transition between Cladocopium and Durusdinium, the process of shuffling from one symbiont genus to another appears to be cost-free for the coral host, and even appears to be associated with lower stress susceptibility. This raises optimism for the future corals, which will probably have to rely on symbiont shuffling more and more to withstand environmental challenges.
随着海面温度升高，许多曾经容纳枝管藻属共生体的珊瑚物种已被耐热的杜氏藻属所占据。在此，我们探究了一个属的共生体基因表达如何随同一珊瑚宿主内另一个共生体属的丰度变化而改变，以及这种相互作用对宿主有何影响。共生体基因表达主要取决于该属在宿主内是少数还是多数，这影响了所有基因的79%（杜氏藻属）和96%（枝管藻属）。在这两个属中，光合作用组件（在少数状态下上调）和可能与细胞运动相关的蛋白质（在多数状态下上调）都观察到了特别强烈的影响。重要的是，当宿主内两个属以相当比例存在时，不存在与混合共生状态相关的独特基因表达特征，这可能导致更激烈的竞争。混合共生也与宿主应激升高无关：事实上，热处理后，与枝管藻属和杜氏藻属占主导的珊瑚相比，混合共生珊瑚的应激特征最低。总之，在枝管藻属和杜氏藻属之间的更替过程中，两个共生体属都经历了广泛且在很大程度上相互的生理转变，但没有证据表明有害于宿主的拮抗相互作用会加剧。除非本研究中的混合共生珊瑚不代表枝管藻属和杜氏藻属之间的典型转变，否则从一个共生体属转变到另一个共生体属的过程对珊瑚宿主似乎没有成本，甚至似乎与较低的应激敏感性相关。这为未来的珊瑚带来了乐观情绪，它们可能不得不越来越多地依靠共生体更替来应对环境挑战。
