A phosphate starvation response gene (psr1-like) is present and expressed in Micromonas pusilla and other marine algae

Abstract

Phosphorus (P) limits primary production in regions of the surface ocean, and many plankton species exhibit specific physiological responses to P-deficiency. The metabolic response of Micromonas pusilla, an ecologically relevant marine photoautotroph, to P-deficiency was investigated using environmental metabolomics and comparative genomics. The concentrations of some intracellular metabolites were elevated in the P-deficient cells (e.g., xanthine, inosine) and genes involved in the associated metabolic pathways shared a predicted conserved amino acid motif in the non-coding regions of each gene. The presence of the conserved motif suggests that these genes may be co-regulated, and the motif may constitute a regulatory element for binding a transcription factor, specifically that of Psr1 (Phosphate starvation response,), first described in the alga, Chlamydomonas reinhardtii. A putative phosphate starvation response gene (psr1-like) was identified in M. pusilla with homology to well characterized psr1/phr1 genes in algae and plants, respectively. This gene appears to be present and expressed in other marine algal taxa (e.g., Emiliania huxleyi) in field sites that are chronically phosphorus-limited. Results from the present study have implications for understanding phytoplankton taxon-specific roles in mediating P cycling in the ocean.