Turmel Monique, Pombert Jean-François, Kosanovic Christina, Julian Alexander Thomas, Otis Christian, Lemieux Claude
Département de Biochimie, de Microbiologie et de Bio-Informatique, Institut de Biologie Intégrative et des Systèmes, Université Laval, Québec, QC G1V 0A6, Canada.
Department of Biology, Illinois Institute of Technology, Chicago, IL, USA.
Genome Biol Evol. 2025 Jul 3;17(7). doi: 10.1093/gbe/evaf140.
The tiny green algae belonging to the class Chloropicophyceae play a key role in marine phytoplankton communities, especially in moderately oligotrophic water; yet, little is known about their biology, lifestyles, and what allows them to thrive in various oceanic environments. A single representative of this class (Chloropicon primus), comprising eight recognized species, has been previously subjected to genome analysis. To gain insight into the evolutionary changes that occurred during speciation in the Chloropicon genus and better understand the genes that distinguish Chloropicon species from other green algae traditionally designated as prasinophytes, we sequenced the genome of a second strain of C. primus and those of three strains of the closely related Chloropicon roscoffensis, the latter species representing the most dominant Chloropicon lineage in oceans. Our analyses highlighted substantial interspecific variations, including differences in chromosome number, gene content, gene arrangement, and ploidy state. Both C. primus genomes were predominantly diploid, while the C. roscoffensis genomes were either haploid or diploid. Specific proteins were identified for each species. Chloropicon roscoffensis possesses a biochemical C4-like inorganic carbon concentrating mechanism that potentially enables recycling of mitochondrial CO2 derived from photorespiration and respiration for carbon fixation in the chloroplast. In addition, it features specific proteins linked to the central carbon metabolism that suggest better coping mechanisms for abiotic stresses compared to C. primus. We also uncovered a previously undescribed eukaryotic recycling pathway for the micronutrient queuosine, a hypermodified nucleoside that is essential for post-transcriptional modification of several tRNAs at their anticodon wobble position.
属于绿球藻纲的微小绿藻在海洋浮游植物群落中起着关键作用，特别是在中度贫营养水域；然而，人们对它们的生物学、生活方式以及它们在各种海洋环境中茁壮成长的原因知之甚少。此前，已对该纲的一个代表物种（原始绿球藻）进行了基因组分析，该纲包含八个已确认的物种。为了深入了解绿球藻属物种形成过程中发生的进化变化，并更好地理解将绿球藻物种与传统上被归类为原绿藻的其他绿藻区分开来的基因，我们对原始绿球藻的第二个菌株以及密切相关的罗斯科夫绿球藻的三个菌株进行了基因组测序，后一个物种代表了海洋中最主要的绿球藻谱系。我们的分析突出了种间的显著差异，包括染色体数目、基因含量、基因排列和倍性状态的差异。两个原始绿球藻基因组主要是二倍体，而罗斯科夫绿球藻基因组要么是单倍体，要么是二倍体。每个物种都鉴定出了特定的蛋白质。罗斯科夫绿球藻拥有一种类似生化C4的无机碳浓缩机制，这可能使光呼吸和呼吸产生的线粒体CO2得以循环利用，用于叶绿体中的碳固定。此外，它还具有与中心碳代谢相关的特定蛋白质，这表明与原始绿球藻相比，它对非生物胁迫具有更好的应对机制。我们还发现了一种以前未描述的真核生物对微量营养素queuosine的循环利用途径，queuosine是一种高度修饰的核苷，对于几种tRNA在其反密码子摆动位置的转录后修饰至关重要。
