Diatoms adapt to various aquatic light environments and play major roles in the global carbon cycle using their unique light-harvesting system, i.e., fucoxanthin chlorophyll a/c binding proteins (FCPs). Structural analyses of photosystem II (PSII)-FCPII and photosystem I (PSI)-FCPI complexes from the diatom Chaetoceros gracilis have revealed the localization and interactions of many FCPs; however, the entire set of FCPs has not been characterized. Here, we identified 46 FCPs in the newly assembled genome and transcriptome of C. gracilis. Phylogenetic analyses suggested that these FCPs could be classified into five subfamilies: Lhcr, Lhcf, Lhcx, Lhcz, and novel Lhcq, in addition to a distinct type of Lhcr, CgLhcr9. The FCPs in Lhcr, including CgLhcr9 and some Lhcqs, had orthologous proteins in other diatoms, particularly those found in the PSI-FCPI structure. By contrast, the Lhcf subfamily, some of which were found in the PSII-FCPII complex, seemed to be diversified in each diatom species, and the number of Lhcqs differed among species, indicating that their diversification may contribute to species-specific adaptations to light. Further phylogenetic analyses of FCPs/light-harvesting complex (LHC) proteins using genome data and assembled transcriptomes of other diatoms and microalgae in public databases suggest that our proposed classification of FCPs was common among various red-lineage algae derived from secondary endosymbiosis of red algae, including Haptophyta. These results provided insights into the loss and gain of FCP/LHC subfamilies during the evolutionary history of the red algal lineage.

中文翻译：

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纤毛角藻岩藻黄质-叶绿素 a/c 蛋白的分子系统发育和 Lhcq/Lhcf 多样性

硅藻适应各种水生光环境，并利用其独特的光收集系统，即岩藻黄质叶绿素a / c结合蛋白 (FCP) ，在全球碳循环中发挥重要作用。来自硅藻Chaetoceros gracilis的光系统 II (PSII)-FCPII 和光系统 I (PSI)-FCPI 复合物的结构分析揭示了许多 FCP 的定位和相互作用。然而，尚未对整个 FCP 集进行表征。在这里，我们在新组装的C. gracilis基因组和转录组中鉴定了 46 个 FCP. 系统发育分析表明，这些 FCP 可分为五个亚科：Lhcr、Lhcf、Lhcx、Lhcz 和新的 Lhcq，此外还有一个独特类型的 Lhcr、CgLhcr9。Lhcr 中的 FCP，包括 CgLhcr9 和一些 Lhcq，在其他硅藻中具有直系同源蛋白，尤其是在 PSI-FCPI 结构中发现的那些。相比之下，Lhcf 亚科（其中一些在 PSII-FCPII 复合体中发现）似乎在每个硅藻物种中都具有多样性，并且 Lhcq 的数量因物种而异，表明它们的多样化可能有助于物种对光的特异性适应. 使用基因组数据和公共数据库中其他硅藻和微藻的组装转录组对 FCPs/光捕获复合物 (LHC) 蛋白进行进一步系统发育分析表明，我们提出的 FCPs 分类在源自红藻二次内共生的各种红系藻类中很常见，包括触生植物。这些结果提供了对红藻谱系进化历史中 FCP/LHC 亚科的丢失和增加的见解。