Diurnal oscillations of metabolite abundances and gene analysis provide new insights into central metabolic processes of the brown alga Ectocarpus siliculosus

• Published in: The New phytologist Vol. 188; no. 1; pp. 98 - 110
• Main Authors: Gravot, Antoine, Dittami, Simon M., Rousvoal, Sylvie, Lugan, Raphael, Eggert, Anja, Collén, Jonas, Boyen, Catherine, Bouchereau, Alain, Tonon, Thierry
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.10.2010; Blackwell Publishing; Blackwell Publishing Ltd; Wiley
• Subjects: Algae; Amino acid metabolism; Amino acids; Amino Acids - metabolism; Bacillariophyceae; Brown algae; brown algae (Phaeophyceae); Carbon; Carbon - metabolism; carbon-concentrating mechanisms; Circadian Rhythm - genetics; Cluster Analysis; Ectocarpus; Ectocarpus siliculosus; Enzymes; Gene Expression Profiling; Genes - genetics; Genomes; Glycolates; Life Sciences; Mannitol - metabolism; Metabolism; metabolite profiling; Metabolome - genetics; Metabolomics; Models, Biological; nyctemeral cycle; Phaeophyceae - genetics; Phaeophyceae - metabolism; Photorespiration; Phytopathology and phytopharmacy; transcriptomic profiling; Vegetal Biology; γ-aminobutyric acid (GABA); Ectocarpus siliculosus; photorespiration,nyctemeral cycle; brown algae (Phaeophyceae); carbon-concentrating mechanisms
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/j.1469-8137.2010.03400.x

Knowledge about primary metabolic processes is essential for the understanding of the physiology and ecology of seaweeds. The Ectocarpus siliculosus genome now facilitates integrative studies of the molecular basis of primary metabolism in this brown alga. Metabolite profiling was performed across two light-dark cycles and under different CO₂ and O₂ concentrations, together with genome and targeted gene expression analysis. Except for mannitol, E. siliculosus cells contain low levels of polyols, organic acids and carbohydrates. Amino acid profiles were similar to those of C3-type plants, including glycine/serine accumulation under photorespiration-enhancing conditions. γ-Aminobutyric acid was only detected in traces. Changes in the concentrations of glycine and serine, genome annotation and targeted expression analysis together suggest the presence of a classical photorespiratory glycolate pathway in E. siliculosus rather than a malate synthase pathway as in diatoms. Several metabolic and transcriptional features do not clearly fit with the hypothesis of an alanine/aspartate-based inducible C4-like metabolism in E. siliculosus. We propose a model in which the accumulation of alanine could be used to store organic carbon and nitrogen during the light period. We finally discuss a possible link between low γ-aminobutyric acid contents and the absence of glutamate decarboxylase genes in the Ectocarpus genome.