The marine eukaryotic alga Heterosigma akashiwo (Raphidophyceae) is known for forming ichthyotoxic harmful algal blooms (HABs). In the past 50 years, H. akashiwo blooms have increased, occurring globally in highly eutrophic coastal and estuarine systems. These systems often incur dramatic physicochemical changes, including macronutrient (nitrogen and phosphorus) enrichment and depletion, on short timescales. Here, H. akashiwo cultures grown under nutrient replete, low N and low P growth conditions were examined for changes in biochemical and physiological characteristics in concert with transcriptome sequencing to provide a mechanistic perspective on the metabolic processes involved in responding to N and P stress. There was a marked difference in the overall transcriptional pattern between low N and low P transcriptomes. Both nutrient stresses led to significant changes in the abundance of thousands of contigs related to a wide diversity of metabolic pathways, with limited overlap between the transcriptomic responses to low N and low P. Enriched contigs under low N included many related to nitrogen metabolism, acquisition, and transport. In addition, metabolic modules like photosynthesis and carbohydrate metabolism changed significantly under low N, coincident with treatment-specific changes in photosynthetic efficiency and particulate carbohydrate content. P-specific contigs responsible for P transport and organic P use were more enriched in the low P treatment than in the replete control and low N treatment. These results provide new insight into the genetic mechanisms that distinguish how this HAB species responds to these two common nutrient stresses, and the results can inform future field studies, linking transcriptional patterns to the physiological ecology of H. akashiwo in situ.

海洋真核生物藻类异弯（Raphidophyceae）是已知的用于形成ichthyotoxic有害藻类（赤潮）。在过去的50年中，赤霞鱼的水华增加了，在全球高度富营养化的沿海和河口系统中都发生了。这些系统通常会在短时间内引起剧烈的物理化学变化，包括大量营养素（氮和磷）的富集和消耗。在这里，赤子华在营养充足，低氮和低磷生长条件下生长的培养物，与转录组测序相结合，研究了生化和生理特性的变化，从而提供了对响应氮和磷胁迫的代谢过程的机械观点。低N和低P转录组之间的总体转录模式存在显着差异。两种养分胁迫都导致与大量代谢途径有关的数千个重叠群的显着变化，对低氮和低磷的转录组反应之间的重叠有限。在低氮下富集的重叠群包括许多与氮代谢，获得有关的和运输。此外，在低氮下，光合作用和碳水化合物代谢等代谢模块发生了显着变化，与光合作用效率和糖类微粒含量的治疗特定变化相吻合。与完全控制和低氮处理相比，低磷处理中负责磷转运和有机磷利用的磷特异性重叠群更为丰富。这些结果提供了新的洞察力，以区分这种HAB物种如何响应这两种常见的营养胁迫的遗传机制，并且这些结果可以为将来的田间研究提供参考，将转录模式与玉米的生理生态联系起来。H. akashiwo原位。