Darkness-induced effects on gene expression in Cosmarium crenatum (Zygnematophyceae) from a polar habitat. Effects of darkness on the gene expression in Cosmarium crenatum

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.