Comparison of Independent Evolutionary Origins Reveals Both Convergence and Divergence in the Metabolic Mechanisms of Symbiosis.
Comparison of Independent Evolutionary Origins Reveals Both Convergence and Divergence in the Metabolic Mechanisms of Symbiosis.
复制标题
独立进化起源的比较揭示了共生代谢机制的趋同和分歧。
DOI：
10.1016/j.cub.2019.11.053
复制
发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Sørensen MES
中科院分区：
文献类型：
--
作者：
Sørensen MES
通过合并以前独立的谱系，共生促进了新特征的获得和难以进入的生态位的开发[1，2]，推动了进化创新和重要的生态系统功能[3-6]。建立的暂时性使共生起源的研究变得困难，但独立起源的实验比较可以揭示支撑机制的收敛程度[7，8]。我们用相互代谢的脉冲追逐方法比较了草履虫的两个独立来源--绿光共生[9-11]的代谢机制。这表明，寄主来源的氮在绿藻类型[12，13]中的营养交换和利用与共生体来源的碳在球囊藻类中的趋同模式[14，15]。与聚合的初级营养交换一致，伙伴交换的宿主-共生体配对是起作用的。含有天然或重组共生菌的寄主与不含等基因共生菌的寄主的直接竞争表明，共生对寄主的适合性收益随着光照的增加而增加，但因基因型而异。全球新陈代谢在绿藻之间的差异比在囊泡类型之间的差异更大，并提出了不同的光管理机制。具体地说，藻类共生体在高光强下产生光保护类胡萝卜素或产生更多的叶绿素，导致寄主-共生体对之间的光合作用效率和非光化学猝灭的相应差异。这些数据表明，Bursaria-ChlorellynBiosis的多重来源使用了趋同的营养交换，而与光共生功能相关的其他光合作用性状则出现了分化。虽然融合可以在不同菌株之间切换伙伴，但由于次要共生性状的差异而导致的表型错配可能在自然界中调节宿主-共生体的专一性。
Through the merger of previously independent lineages, symbiosis promotes the acquisition of new traits and exploitation of inaccessible ecological niches [1, 2], driving evolutionary innovation and important ecosystem functions [3–6]. The transient nature of establishment makes study of symbiotic origins difficult, but experimental comparison of independent origins could reveal the degree of convergence in the underpinning mechanisms [7, 8]. We compared the metabolic mechanisms of two independent origins ofParamecium bursaria-Chlorellaphotosymbiosis [9–11] using a reciprocal metabolomic pulse-chase method. This showed convergent patterns of nutrient exchange and utilization for host-derived nitrogen in theChlorellagenotypes [12, 13] and symbiont-derived carbon in theP. bursariagenotypes [14, 15]. Consistent with a convergent primary nutrient exchange, partner-switched host-symbiont pairings were functional. Direct competition of hosts containing native or recombined symbionts against isogenic symbiont-free hosts showed that the fitness benefits of symbiosis for hosts increased with irradiance but varied by genotype. Global metabolism varied more between theChlorellathan theP. bursariagenotypes and suggested divergent mechanisms of light management. Specifically, the algal symbiont genotypes either produced photo-protective carotenoid pigments at high irradiance or more chlorophyll, resulting in corresponding differences in photosynthetic efficiency and non-photochemical quenching among host-symbiont pairings. These data suggest that the multiple origins ofP. bursaria-Chlorellasymbiosis use a convergent nutrient exchange, whereas other photosynthetic traits linked to functioning of photosymbiosis have diverged. Although convergence enables partner switching among diverse strains, phenotypic mismatches resulting from divergence of secondary symbiotic traits could mediate host-symbiont specificity in nature.