An integrated analysis of phosphorus starvation responses in the diatom Pheaodactylum tricornutum

48 h and 72 h after P, transcriptional profiles of P-depleted (-P) and P-replete (+P) cultures depletion were integrated with metabolite and physiological data. It resulted in identification of essential metabolic pathway remodeled under P deficiency. The most significant inductions were related to proteins involved in phosphate acquisition and scavenging, such as phosphate transporters, alkaline phosphatases and nucleotidases. P-depleted cells also showed photosynthesis, nitrogen assimilation, and nucleic acid and ribosome biosynthesis. Repression of the Calvin cycle along with induction of cytosolic glycolysis and the pentose phosphate pathway led to carbon reallocation. Furthermore, we observed changes in the lipid composition of P-depleted cultures through degradation of phospholipids and induction of biosynthetic pathways of non-phosphorus containing lipids. Axenic cultures of Phaeodactylum tricornutum were grown in f/2 medium and kept in exponential growth at 15ºC under continuous white fluorescent light (60 µmol photons m-2 s-1) inside the shaking incubator for three weeks. Three replicates and parallels of the start culture were transferred to media supplemented with complete f/2 nutrients (replete) or f/2 without phosphate (deplete). Cells were incubated in batch cultures with a start cell density of 5×104 ml-1 in 75 cm2 sterile culture flasks and volume of 220 ml. Cell counting and variable in vivo Chl a fluorescence (Fv/Fm) was measured daily. For the other experiments, samples were harvested 48 h and 72 h after the beginning of the treatment.