Light-Dependent Transcriptional Regulation of Genes of Biogeochemical Interest in the Diploid and Haploid Life Cycle Stages of Emiliania huxleyi

Abstract

The expression of genes of biogeochemical interest in calcifying and noncalcifying life stages of the coccolithophore Emiliania huxleyi was investigated. Transcripts potentially involved in calcification were tested through a light-dark cycle. These transcripts were more abundant in calcifying cells and were upregulated in the light. Their application as potential candidates for in situ biogeochemical proxies is also suggested.Phytoplankton productivity and calcification are two major biological processes contributing to the regulation of the climate of our planet via their impact on the global carbon cycle.Coccolithophores are planktonic unicellular microalgae which play an important role in ocean biogeochemistry (20). They are among the most productive calcifying organisms on Earth and thus are a key functional group in the marine carbon cycle.Among modern coccolithophorids, Emiliania huxleyi is the most successful species, exhibiting a worldwide distribution in open and coastal oceans, except in the polar areas.Emiliania huxleyi has been intensively studied in several contexts, but its physiology at the molecular level remains largely unknown. However, this area can now be intensively investigated thanks to the ever-growing number of analyses of expressed sequence tags (6,10,21,27) and the whole-genomeannotation effort (Joint Genome Institute).In this exploratory work, we focus on a few genes potentially involved in calcification, one of the processes which will likely be affected by current and future global environmental changes, such as ocean acidification.Previous molecular studies of E. huxleyi calcification (4, 17, 21) were carried out using noncalcifying and calcifying cultures obtained by inducing phosphorus limitation. In this paper, we take advantage of the fact that the haplodiploid life cycle of E. huxleyi involves an alternation between calcified, coccolithbearing diploid cells and organic scale-bearing motile haploid cells, each of which can exist independently of the other and reproduce vegetatively (8). This approach has the considerable advantage of maintaining the two life stages of E. huxleyi under identical culture conditions.While the large subunit of RuBisCO (ribulose-1,5-bisphosphate carboxylase), rbcL, is well known for its central role in photosynthetic carbon fixation and has already been shown in a pilot field experiment to relate successfully to photosynthesis measurements (1), research aimed at identifying key genes and proteins involved in calcification is still in its infancy.In the last few years, several novel molecular tools have been used to investigate calcification and coccolithogenesis (4,6,17,21,27). Results from these studies of coccolithophores as well as those carried out with other calcifying organisms were used to select genes. gpa was chosen because it codes for proteins in association with intracellular precursors of coccolith polysaccharides (2). The carbonic anhydrase (CA) proteins play an important role in the biomineralization of vertebrates and invertebrates ...

Expression of biomineralization‐related ion transport genes in Emiliania huxleyi

“…GPA gene transcripts were approximately twice as abundant in haploid than diploid cells, suggesting a role for GPA in the absence of calcification. von Dassow and colleagues (2009) confirmed the presence of haploid expression of GPA in RCC1217 via non‐quantitative RT‐PCR and Richier and colleagues (2009) found GPA expression to be relatively stable between the diploid RCC1216 and haploid RCC1217 strains. The discrepancy between our GPA expression data and the data presented in Richier and colleagues (2009) may relate to important differences in the normalization procedures used for gene expression, with Richier and colleagues (2009) normalizing to total RNA rather than ERGs.…”

“…von Dassow and colleagues (2009) confirmed the presence of haploid expression of GPA in RCC1217 via non‐quantitative RT‐PCR and Richier and colleagues (2009) found GPA expression to be relatively stable between the diploid RCC1216 and haploid RCC1217 strains. The discrepancy between our GPA expression data and the data presented in Richier and colleagues (2009) may relate to important differences in the normalization procedures used for gene expression, with Richier and colleagues (2009) normalizing to total RNA rather than ERGs. Remarkably, GPA transcripts were strongly repressed in calcifying diploid cells with a ∼26‐fold downregulation relative to non‐calcifying diploid cells and a ∼10.8 downregulation relative to cells in 0 mM Ca 2+ .…”

The Divergence, Actions, Roles, and Relatives of Sodium-Coupled Bicarbonate Transporters

“…3) A number of overlapping and nonoverlapping Slc4-like sequence fragments have been identified in the genome of the phytoplankter Emilyiana huxleyi (621,795). Analysis of these fragments suggests that they might be derived from more than two, and perhaps as many as four, Slc4-like genes.…”

Sorting duplicated loci disentangles complexities of polyploid genomes masked by genotyping by sequencing

“…Fins & Seeb ; Richier et al . ), enabling unambiguous genotyping and map‐based genomic study (Eckert et al . ; Sork et al .…”