Table_1_Transcriptomic responses to shifts in light and nitrogen in two congeneric diatom species.XLSX

Light and nitrogen availability are basic requirements for photosynthesis. Changing in light intensity and nitrogen concentration may require adaptive physiological and life process changes in phytoplankton cells. Our previous study demonstrated that two Thalassiosira species exhibited, respectively, distinctive physiological responses to light and nitrogen stresses. Transcriptomic analyses were employed to investigate the mechanisms behind the different physiological responses observed in two diatom species of the genus Thalassiosira. The results indicate that the congeneric species are different in their cellular responses to the same shifting light and nitrogen conditions. When conditions changed to high light with low nitrate (HLLN), the large-celled T. punctigera was photodamaged. Thus, the photosynthesis pathway and carbon fixation related genes were significantly down-regulated. In contrast, the small-celled T. pseudonana sacrificed cellular processes, especially amino acid metabolisms, to overcome the photodamage. When changing to high light with high nitrate (HLHN) conditions, the additional nitrogen appeared to compensate for the photodamage in the large-celled T. punctigera, with the tricarboxylic acid cycle (TCA cycle) and carbon fixation significantly boosted. Consequently, the growth rate of T. punctigera increased, which suggest that the larger-celled species is adapted for forming post-storm algal blooms. The impact of high light stress on the small-celled T. pseudonana was not mitigated by elevated nitrate levels, and photodamage persisted.

光照与氮素可利用性是光合作用的基本必要条件。光照强度与氮浓度的变化，可促使浮游植物细胞发生适应性生理与生命过程调整。我们此前的研究表明，两种角毛藻属(Thalassiosira)藻类分别对光照与氮胁迫表现出迥异的生理响应。本研究采用转录组分析(transcriptomic analyses)技术，探究了两种角毛藻属硅藻(diatom)对光照与氮胁迫产生不同生理响应的内在机制。研究结果显示，该同属物种在相同的光照与氮条件波动下，细胞响应模式存在显著差异。当环境转变为高光低硝酸盐条件（high light with low nitrate, HLLN）时，大细胞型的点刺角毛藻(T. punctigera)发生光损伤，其光合作用通路与固碳相关基因的表达量显著下调。与之相反，小细胞型的假微型海链藻(T. pseudonana)则牺牲部分细胞过程（尤其是氨基酸代谢）以抵御光损伤。当环境转变为高光高硝酸盐条件（high light with high nitrate, HLHN）时，额外的氮源似乎弥补了大细胞型点刺角毛藻的光损伤，其三羧酸循环(tricarboxylic acid cycle, TCA循环)与固碳过程显著增强，点刺角毛藻的生长速率随之提升，这表明该大细胞型物种适应于风暴后藻华的形成。而高硝酸盐浓度并未缓解高光胁迫对小细胞型假微型海链藻的影响，其光损伤持续存在。