Research

Transcriptome analysis of functional differentiation between haploid and diploid cells of Emiliania huxleyi, a globally significant photosynthetic calcifying cell

Peter von Dassow¹ , Hiroyuki Ogata² , Ian Probert¹ , Patrick Wincker³ , Corinne Da Silva³ , Stéphane Audic² , Jean-Michel Claverie² and Colomban de Vargas¹

¹  Evolution du Plancton et PaleOceans, Station Biologique de Roscoff, CNRS UPMC UMR7144, 29682 Roscoff, France

²  Information Génomique et Structurale, CNRS - UPR2589, Institut de Microbiologie de la Méditerranée, Parc Scientifique de Luminy - 163 Avenue de Luminy - Case 934, FR- 13288, Marseille cedex 09, France

³  Genoscope, 2 Rue Gaston Crémieux, 91057 Evry, France

author email corresponding author email

Genome Biology 2009, 10:R114doi:10.1186/gb-2009-10-10-r114

Published:	15 October 2009

Subject areas: Ecology, Genome studies, Microbiology and parasitology

Abstract

Background

Eukaryotes are classified as either haplontic, diplontic, or haplo-diplontic, depending on which ploidy levels undergo mitotic cell division in the life cycle. Emiliania huxleyi is one of the most abundant phytoplankton species in the ocean, playing an important role in global carbon fluxes, and represents haptophytes, an enigmatic group of unicellular organisms that diverged early in eukaryotic evolution. This species is haplo-diplontic. Little is known about the haploid cells, but they have been hypothesized to allow persistence of the species between the yearly blooms of diploid cells. We sequenced over 38,000 expressed sequence tags from haploid and diploid E. huxleyi normalized cDNA libraries to identify genes involved in important processes specific to each life phase (2N calcification or 1N motility), and to better understand the haploid phase of this prominent haplo-diplontic organism.

Results

The haploid and diploid transcriptomes showed a dramatic differentiation, with approximately 20% greater transcriptome richness in diploid cells than in haploid cells and only ≤ 50% of transcripts estimated to be common between the two phases. The major functional category of transcripts differentiating haploids included signal transduction and motility genes. Diploid-specific transcripts included Ca²⁺, H⁺, and HCO₃^- pumps. Potential factors differentiating the transcriptomes included haploid-specific Myb transcription factor homologs and an unusual diploid-specific histone H4 homolog.

Conclusions

This study permitted the identification of genes likely involved in diploid-specific biomineralization, haploid-specific motility, and transcriptional control. Greater transcriptome richness in diploid cells suggests they may be more versatile for exploiting a diversity of rich environments whereas haploid cells are intrinsically more streamlined.