Calcium-related genes associated with intracellular calcification of Emiliania huxleyi (Haptophyta) CCMP 371

Emiliania huxleyi (a haptophyte) is the most abundant coccolithophore species that produces delicate calcite scales called coccoliths.In this study, we identified several candidate genes associated with coccolith production by comparing the transcriptomes of the calcifying (CCMP 371) and non-calcifying (CCMP 2090) strains of E. huxleyi.Among the candidates, genes highly expressed in CCMP 371 were identified.To confirm whether these genes are associated with calcification, we modulated coccolith production in CCMP 371 by culturing it at different calcium concentrations.At an ambient (10 mM) concentration of calcium in the growth medium, CCMP 371 sustained its calcifying ability.However, at a low (0.1 mM) concentration or absence of calcium, there was no calcite formation, demonstrating that calciumlimiting conditions negatively affect calcification.We also evaluated the expression patterns of the putative genes in cells grown at different calcium concentrations by quantitative reverse transcription polymerase chain reaction.In addition, we showed that the growth rate of cells cultured under calcium-limiting conditions does not differ from that under ambient conditions.Further studies are required to investigate the roles of the putative calcification-associated genes at the molecular level.