Table_3_Transcriptomic Responses of Four Pelagophytes to Nutrient (N, P) and Light Stress.xlsx

Pelagophytes are abundant picophytoplankton within open ocean ecosystems and the causative algae of harmful brown tide blooms in estuaries. The physiological capabilities facilitating the ecological success of pelagophytes in these diverse ecosystems remains poorly understood. Here, we investigated the transcriptional response of two coastal pelagophytes (Aureococcus anophagefferens and Aureoumbra lagunensis) and two open ocean pelagophytes (Pelagococcus subviridis and Pelagomonas calceolata) to conditions commonly found within the marine ecosystems where they thrive: low concentrations of nitrogen (N), phosphorus (P), or light. OrthoMCL was used to generate a total of 62,653 orthologous groups (OGs) with only a small fraction of these OGs (2,776 or 4.4%) being shared among all four pelagophytes. Of the commonly shared OGs, 8% were significantly differentially abundant under low N, P, or light with the majority associated with energy and lipid metabolism. Distinct responses among pelagophytes included increased abundance of transcripts encoding phosphate transporters (Aureococcus) and transcripts encoding a pyrophosphatase (Aureococcus and Pelagomonas) under low P, the expression of a suite of organic nitrogen-degrading enzymes under low N (Aureoumbra and Pelagomonas), increased abundance of transcripts encoding flavodoxins relative to ferredoxins (Pelagomonas) and transcripts encoding lysophospholipase (Pelagococcus) under low light, and both increases and decreases in abundance of transcripts encoding selenoproteins in all pelagophytes except Pelagococcus. Collectively, this study provides new information on the expressed gene compliment of these poorly characterized taxa and demonstrates that these pelagophytes possess a combination of shared and unique physiological features that likely facilitate their adaptation to distinct environmental conditions.

远洋藻类（pelagophytes）是开阔海洋生态系统中广泛分布的超微型浮游植物（picophytoplankton），同时也是引发河口有害褐潮爆发的致病藻类。目前学界对支撑远洋藻类在这类多样生态系统中取得生态成功的生理机制仍知之甚少。本研究针对两种沿岸远洋藻类（Aureococcus anophagefferens 与 Aureoumbra lagunensis）以及两种开阔海洋远洋藻类（Pelagococcus subviridis 与 Pelagomonas calceolata），探究其在各自栖息的海洋生态系统中常见的低浓度氮（N）、磷（P）或光照条件下的转录响应。本研究使用OrthoMCL软件共构建了62653个同源基因簇（orthologous groups, OGs），其中仅有极小一部分（2776个，占比4.4%）为四种远洋藻类所共有。在共有同源基因簇中，8%在低氮、低磷或低光照条件下发生了显著的表达丰度变化，其中大部分与能量代谢及脂质代谢相关。不同远洋藻类间的响应模式存在显著差异：低磷条件下，Aureococcus anophagefferens 中编码磷酸盐转运蛋白（phosphate transporters）的转录本丰度显著上调，Aureococcus anophagefferens 与 Pelagomonas calceolata 中编码焦磷酸酶（pyrophosphatase）的转录本丰度亦显著提升；低氮条件下，Aureoumbra lagunensis 与 Pelagomonas calceolata 会表达一系列有机氮降解酶（organic nitrogen-degrading enzymes）；低光照条件下，Pelagomonas calceolata 中编码黄素氧还蛋白（flavodoxins）的转录本丰度相较于铁氧还蛋白（ferredoxins）显著升高，而Pelagococcus subviridis 中编码溶血磷脂酶（lysophospholipase）的转录本丰度上调；除Pelagococcus subviridis 外的所有远洋藻类中，编码硒蛋白（selenoproteins）的转录本丰度均出现了上调与下调的双向变化。综上，本研究为这些研究程度较低的类群的表达基因谱提供了新的认知，并证实这些远洋藻类兼具共有与独特的生理特征，这些特征或助力其适应不同的环境条件。