Darkness-induced effects on gene expression in Cosmarium crenatum (Zygnematophyceae) from a polar habitat

Light is a key environmental regulator in all photosynthetic organisms. Many studies focused on the physiologic response to changes in light availability of species from the Zygnematophyceae, but the impact of the absence of light and the molecular acclimation process have been poorly understood. Here we present transcriptomic analyses of Cosmarium crenatum from a polar habitat exposed to darkness. The algae were cultured in dark for one week; cell number and quantum yield of photosystem II (Fv/Fm) were monitored. Cell number was stable in darkness, but the Fv/Fm decreased in both groups, darkness-treated and control. Gene expression analysis revealed a strong repression of transcripts associated with photosynthesis, photorespiration and cell wall development. Carbohydrate and lipid metabolism were differentially regulated, but starch is shown to be the primary energy source in darkness. Additionally, C. crenatum induced mRNA correlated with histone modifications which may be a specific response to an adaption and acclimation to polar conditions. Our study sheds light on the molecular acclimation processes to darkness and provides ecological implications for new perspectives in this specialized group of green algae.

光是所有光合生物的关键环境调控因子。既往诸多研究聚焦于双星藻纲（Zygnematophyceae）物种对光照条件变化的生理响应，但针对黑暗环境的影响及其分子适应过程的认知仍较为匮乏。本研究针对采自极地生境的具齿鼓藻（Cosmarium crenatum）开展黑暗处理下的转录组分析：将该藻类暗培养一周，同时监测细胞数量与光系统II（PSII）的量子产量（Fv/Fm）。结果显示，黑暗处理组与对照组的细胞数量均保持稳定，但两组的Fv/Fm均出现下降。基因表达分析表明，与光合作用、光呼吸及细胞壁发育相关的转录本受到显著抑制。碳水化合物与脂质代谢呈现差异化调控，而淀粉被证实为黑暗环境下的主要能量来源。此外，具齿鼓藻诱导了与组蛋白修饰相关的mRNA表达，这可能是其适应极地环境的特异性响应机制。本研究阐明了黑暗环境下的分子适应过程，为这类特化绿藻的研究提供了新的生态学视角与理论参考。