TOR signaling in the smallest free-living photosynthetic eukaryote

CALO G; MARÍA AGUSTINA DE MARCO; SALERNO G; MARTÍNEZ NOËL G

Lisboa

Workshop; EMBO workshop Target of Rapamycin in photosynthetic organisms; 2021

EMBO

Target of rapamycin (TOR) is a master regulator that controls growth and metabolism by integrating external and internal signals in all eukaryotic species. TOR kinase regulates the balance between anabolic and catabolic processes to assure energy homeostasis. To gain insights in TOR signaling in photosynthetic eukaryotes we studied the TOR signaling in Ostreococcus tauri, the smallest free-living eukaryote described so far. This picoalga is particularly important because it has a key site at the base of the green lineage and it is part of the marine phytoplankton, contributing to global photosynthesis. Therefore, we investigated the TOR complex conservation in Ostreococcus by using first and second generation TOR inhibitors. We analyzed the effect of TOR downregulation on cell growth, on photosynthetic parameters and on the accumulation of carbon reserves such as lipids and starch. Results showed that Ostreococcus responds to TOR inhibitors more similarly to plant kinase than to that of the model green algae Chlamydomonas reinhardtii. We also evaluated OtTOR expression in response to nutritional stress conditions and demonstrated that the kinase is tightly regulated. Besides, we studied the effect of positive regulators of plant TOR kinase such as sugars and growth-promoting hormones. Taken together, our data indicate that TOR signaling is conserved in the plant lineage and in Ostreococcus, showing some specific features. Thus, we propose this unicellular green alga as a good and simple model for studying TOR kinase and its regulation.Supported by CONICET, ANPCyT, UNMdP.