Inositol polyphosphates regulate resilient mechanisms in the green alga Chlamydomonas reinhardtii to adapt to extreme nutrient conditions.

In the context of climate changing environments, microalgae can be excellent organisms to understand molecular mechanisms that activate survival strategies under stress. Chlamydomonas reinhardtii signalling mutants are extremely useful to decipher which strategies photosynthetic organisms use to cope with changeable environments. The mutant vip1-1 has an altered profile of pyroinositol polyphosphates (PP-InsPs), which are signalling molecules present in all eukaryotes and have been connected to P signalling in other organisms including plants, but their implications in other nutrient signalling are still under evaluation. In this study, we conducted prolonged starvation in WT and vip1-1 Chlamydomonas cells. After N and P had been consumed, they showed important differences in the levels of chlorophyll, photosystem II (PSII) activity and ultrastructural morphology, including differences in the cell size and cell division. Metabolomic analysis under these conditions revealed an overall decrease in different organic compounds such as amino acids, including arginine and its precursors and tryptophan, which is considered a signalling molecule itself in plants. In addition, we observed significant differences in RNA levels of genes related to N assimilation that are under the control of the NIT2 transcription factor. These data are of important relevance in understanding the signalling role of PP-InsPs in nutrient sensing, especially regarding N, which has not directly been connected to these molecules in green organisms before. Additionally, the PP-InsPs regulation over cell size and photosynthesis supports novel strategies for the generation of resilient strains, expanding the biotechnological applications of green microalgae.