Abstract
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 on the other side 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, 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. General carbohydrate and lipid metabolism were differentially regulated, but starch is shown to be the primary energy source in these conditions. Additionally, C. crenatum induced mRNA responsible for epigenetic modifications which may be a specific response to an adaption and acclimation to polar conditions. Our study sheds light on the molecular acclimation process to darkness and provides ecological implications for new perspectives in this specialized group of green algae.
Highlights
Numerous studies showed that light is a key regulator of plant metabolism, development and a central factor for survival
This study aims to characterize the molecular response to long-term darkness-induced changes in gene expression in the non-model microalga C. crenatum
We present a comprehensive de novo reference transcriptome from C. crenatum under 18 different temperature and light regimes, covering initial, short-term and long-term acclimation
Summary
Numerous studies showed that light is a key regulator of plant metabolism, development and a central factor for survival. Described as an essentially arctic-alpine species, C. crenatum is predominantly found under harsh climatic conditions of high altitude or latitude, but exhibits a great acclimation potential, and may be encountered even in the lowlands[18] In these wide-spread localities environmental factors like temperature and nutrients differ tremendously, but the availability of light may be the most challenging factor for a photoautotroph. It is our key hypothesis that an extensive remodeling of the transcriptome is necessary for the alga for survival during elongated darkness as photosynthesis cannot be the energy source It is our long-term goal to understand the molecular basis of acclimation to environmental alterations like the influence of polar night. Physiological responses to darkness of one week were determined by cell growth and the maximum quantum yield of photosystem II and compared to gene expression changes
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