Environmental and Evolutionary Genomics Section, Institut de Biologie de l'Ecole Normale Supéreure, CNRS UMR8186 INSERM U1024, Ecole Normale Supérieure, Paris, France.
Mol Biol Evol. 2012 Jan;29(1):367-79. doi: 10.1093/molbev/msr223. Epub 2011 Sep 8.
Diatoms and other chlorophyll-c containing, or chromalveolate, algae are among the most productive and diverse phytoplankton in the ocean. Evolutionarily, chlorophyll-c algae are linked through common, although not necessarily monophyletic, acquisition of plastid endosymbionts of red as well as most likely green algal origin. There is also strong evidence for a relatively high level of lineage-specific bacterial gene acquisition within chromalveolates. Therefore, analyses of gene content and derivation in chromalveolate taxa have indicated particularly diverse origins of their overall gene repertoire. As a single group of functionally related enzymes spanning two distinct gene families, fructose 1,6-bisphosphate aldolases (FBAs) illustrate the influence on core biochemical pathways of specific evolutionary associations among diatoms and other chromalveolates with various plastid-bearing and bacterial endosymbionts. Protein localization and activity, gene expression, and phylogenetic analyses indicate that the pennate diatom Phaeodactylum tricornutum contains five FBA genes with very little overall functional overlap. Three P. tricornutum FBAs, one class I and two class II, are plastid localized, and each appears to have a distinct evolutionary origin as well as function. Class I plastid FBA appears to have been acquired by chromalveolates from a red algal endosymbiont, whereas one copy of class II plastid FBA is likely to have originated from an ancient green algal endosymbiont. The other copy appears to be the result of a chromalveolate-specific gene duplication. Plastid FBA I and chromalveolate-specific class II plastid FBA are localized in the pyrenoid region of the chloroplast where they are associated with β-carbonic anhydrase, which is known to play a significant role in regulation of the diatom carbon concentrating mechanism. The two pyrenoid-associated FBAs are distinguished by contrasting gene expression profiles under nutrient limiting compared with optimal CO2 fixation conditions, suggestive of a distinct specialized function for each. Cytosolically localized FBAs in P. tricornutum likely play a role in glycolysis and cytoskeleton function and seem to have originated from the stramenopile host cell and from diatom-specific bacterial gene transfer, respectively.
硅藻和其他含有叶绿素 c 或 chromalveolate 的藻类是海洋中生产力最高和最多样化的浮游植物之一。从进化的角度来看，叶绿素 c 藻类通过共同的，尽管不一定是单系的，获得红藻以及最有可能的绿藻起源的质体内共生体联系在一起。chromalveolates 中也有强烈的证据表明存在相对高水平的谱系特异性细菌基因获得。因此，对 chromalveolate 分类群中的基因内容和衍生进行分析表明，它们的整体基因库具有特别多样化的起源。作为跨越两个不同基因家族的功能相关酶的单一功能群，果糖 1,6-二磷酸醛缩酶 (FBA) 说明了特定进化关联对硅藻和其他 chromalveolates 与各种带有质体和细菌内共生体的核心生化途径的影响。蛋白质定位和活性、基因表达和系统发育分析表明，双壳硅藻 Phaeodactylum tricornutum 含有五个 FBA 基因，它们的整体功能重叠很小。P. tricornutum 的三个 FBA，一个 I 类和两个 II 类，是质体定位的，每个似乎都有一个独特的进化起源和功能。I 类质体 FBA 似乎是 chromalveolates 从红藻内共生体获得的，而 II 类质体 FBA 的一个拷贝可能起源于古老的绿藻内共生体。另一个拷贝似乎是 chromalveolate 特异性基因复制的结果。质体 FBA I 和 chromalveolate 特异性质体 II 质体 FBA 定位于叶绿体的淀粉核区域，在那里它们与 β-碳酸酐酶相关联，β-碳酸酐酶已知在调节硅藻的碳浓缩机制中起着重要作用。两个与淀粉核相关的 FBA 之间的区别在于在营养限制与最佳 CO2 固定条件相比时，基因表达谱不同，表明每个基因都具有独特的专门功能。P. tricornutum 中的细胞质定位 FBA 可能在糖酵解和细胞骨架功能中发挥作用，并且似乎分别源自 strep 植物宿主细胞和硅藻特异性细菌基因转移。
