Photoperiodic transcriptional responses in Ostreococcus tauri

Although it is well established the seasonal effect of the photoperiod over the transcriptional expression patterns in plants, this effect has not been studied in microalgae. Here we fill the gap using the model microalgae Ostreococcus tauri. Ostreococcus tauri sequenced strain RCC4221 was cultivated in 1.8L column photochemostats operating in continous mode at 20ºC and pH 8 with air bubbling to enable culture homogenization. Media was added at a dilution rate of 0.4 day-1. After four weeks entrainment under long day conditions (16h light : 8 hours dark) or short day conditions (8h light: 16 hours dark) samples were collected every four hours during three days. Subsequently, samples were collected for two days every four hours under free running conditions consisting in continous light. The growth media was prepared using Artificial Sea Water (24.55g NaCl, 0.75g KCl, 4.07g MgCl2·6H2O, 1.47g CaCl2 ·2H2O, 6.04g MgSO4·7H2O and 0.21g NaHCO3 per 1L distilled water) supplemented with 1 mL of Solution I (100g NaNO3 in 250mL distilled water), 1mL of Solution II (700mg Na2HPO4 and 2.5g K2HPO4 in 250mL distilled water) and 1mL of Solution III with trace metals (2.68g NH4Cl, 5.2g Fe-EDTA, 37.2g Na2 -EDTA, 23mg ZnSO4, 14mg CoSO4 , 7.89mg Na2 MoO4 ·2H2O, 2.5mg CuSO4 , 1.7mg H2SeO3 and 180mg MnCl2·4H2O in 500mL distilled water).