Evaluation of actin as a reference for quantitative gene expression studies in Emiliania huxleyi (Prymnesiophyceae) under ocean acidification conditions

Abstract

Gene expression studies of marine phytoplankton under ocean acidification conditions are frequently based on relative measurements, with actin commonly used as a reference gene. Evidence from other organisms suggests that actin gene expression may be regulated by environmental conditions, compromising the role of actin as a reference gene. In this work the reliability of actin as a reference gene for ocean acidification experimental conditions (high CO2 vs low CO2) in two different metabolic states (acclimated metabolism vs perturbed metabolism) for the coccolithophore Emiliania huxleyi was tested. The transcriptional response of the actin (act) is compared with the expression of specific target genes associated with inorganic carbon uptake (α-carbonic anhydrase: αca1) and assimilation (RuBisCO: rbcL), which was regulated under the experimental conditions. Our results showed act expression instability in experimental conditions, evidencing that act is not a reliable reference gene for studies assessing the effect of ocean acidification on Emiliania huxleyi. Furthermore, when the act-based normalization was quantitatively tested, rbcL and αca1 expression were compromised, leading us to conclude that absolute gene expression quantification should be considered as a potentially reliable alternative for studying gene expression under ocean acidification conditions.