Bedera-Garcia, R. | bioRxiv Science

bioRxiv2026

Inositol Pyrophosphates Mediate Chloroplast Lipid Remodeling and Nuclear Gene Repression during High-Light Acclimation in Chlamydomonas reinhardtii

Microalgae are photosynthetic organisms capable of autotrophic growth. Their applicability in multiple industrial fields has been largely studied, thanks to their ability to fixate CO2 into high added value organic products like fatty acids and carotenoids. However, our understanding of the cellular signaling networks that control carbon flux and acclimation to environmental stress remains incomplete. In this study, we used the Chlamydomonas reinhardtii mutant strain vip1-1, which carries a loss-of-function mutation in the hexakisphosphate kinase re-sponsible for the synthesis of inositol pyrophosphates InsP7 and InsP8 (PP-InsPs), to investi-gate the role of these molecules during high-light acclimation. Our results indicate that PP-InsPs participate in the regulation of carbon storage in the form of starch and their deficiency increases TAGs levels in the algal cells. They also impact chloroplast-specific lipid remodeling by modifying membrane composition and fluidity through fatty acid desaturations and glycer-olipid composition. In addition, our findings suggest that PP-InsPs are involved in chloroplast-nucleus communication, where they coordinate transcriptional repression of photosynthesis associated nuclear genes (PhANGs), fatty acid desaturases and lipid synthases, contributing to cellular acclimation to high light. We also found that PP-InsPs modulating effect extended to protein synthesis and accumulation of Calvin-Benson-Bassham cycle intermediates. Therefore, we propose that PP-InsPs function as integratory molecules that balance carbon allocation between storage and structural pools, in response to environmental cues such as high light. These data uncover a novel function of PP-InsPs in high light acclimation and po-tentially in chloroplast-nucleus communication, providing new insights that may help engineering more resilient and efficient strains.

plant biology↗

bioRxiv2024

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

In the actual context of climate changing environments, photosynthetic organisms need to adapt to more extreme conditions. Microalgae can be excellent organisms to understand molecular mechanisms that activate survival strategies under stress. Chlamydomonas reinhardtii signaling mutants are extremely useful to decipher which strategies they use to cope with changeable environments. In this study, we conducted prolonged starvation in wild type and vip1-1 Chlamydomonas cells. The mutant vip1-1 has an altered profile of pyroinositol polyphosphates (PP-InsPs) which are signaling molecules present in all eukaryotes. These molecules have been connected to P signaling in other organisms including plants but their implications in other nutrient signaling is still under evaluation. After prolonged starvation, WT and vip1-1 showed important differences in the levels of chlorophyll and photosystem II (PSII) activity. We also performed a metabolomic analysis under these conditions and found an overall decrease in different organic compounds such as amino acids including arginine and its precursors and tryptophan which is considered as a signaling molecule itself in plants. In addition, we observed significant differences in RNA levels of genes related to nitrogen assimilation that are under the control of NIT2 transcription factor. Overall our data indicate an important role of PP-InsPs in the regulation of nutrient starvation especially regarding N assimilation and C distribution. These data are of great importance for the generation of resilient strains to be used in open ponds and high capacity bioreactors.

plant biology↗