Abstract

The haptophyte alga Emiliania huxleyi is the most abundant coccolithophore in the modern ocean and produces elaborate calcite crystals, called coccolith, in a separate intracellular compartment known as the coccolith vesicle. Despite the importance of biomineralization in coccolithophores, the molecular mechanism underlying it remains unclear. Understanding this precise machinery at the molecular level will provide the knowledge needed to enable further manipulation of biomineralization. In our previous study, altering the calcium concentration modified the calcifying ability of E. huxleyi CCMP371. Therefore in this study, we tested E. huxleyi cells acclimated to three different calcium concentrations (0, 0.1, and 10 mM). To understand the whole transcript profile at different calcium concentrations, RNA-sequencing was performed and used for de novo assembly and annotation. The differentially expressed genes (DEGs) among the three different calcium concentrations were analyzed. The functional classification by gene ontology (GO) revealed that ‘intrinsic component of membrane’ was the most enriched of the GO terms at the ambient calcium concentration (10 mM) compared with the limited calcium concentrations (0 and 0.1 mM). Moreover, the DEGs in those comparisons were enriched mainly in ‘secondary metabolites biosynthesis, transport and catabolism’ and ‘signal transduction mechanisms’ in the KOG clusters and ‘processing in endoplasmic reticulum’, and ‘ABC transporters’ in the KEGG pathways. Furthermore, metabolic pathways involved in protein synthesis were enriched among the differentially expressed proteins. The results of this study provide a molecular profile for understanding the expression of transcripts and proteins in E. huxleyi at different calcium concentrations, which will help to identify the detailed mechanism of its calcification.

Highlights

  • Coccolithophores are major biogenic calcite producers among the unicellular marine phytoplankton

  • In our previous study [16], E. huxleyi CCMP371 cells cultured in 0 mM, 0.1 mM, and 10 mM calcium concentrations showed no coccolith formation under limited-calcium conditions ([Ca2+] 0 and 0.1 mM)

  • We performed RNA sequencing (RNA-seq) analysis of E. huxleyi CCMP371 cells cultured at different calcium concentrations (0, 0.1, and 10 mM)

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Summary

Introduction

Coccolithophores are major biogenic calcite producers among the unicellular marine phytoplankton. Elaborate calcium carbonate scales called coccoliths are produced by these organisms. Each calcite crystal is formed under the stringent control of an intracellular biological. Transcriptome profile of Emiliania huxleyi at different calcium concentrations. Oceans and the Polar Regions of the National Research Foundation of Korea Nrf.re.kr) funded by the Ministry of Science, ICT (2015M1A5A1037053) The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

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