Changes in lipid and carotenoid metabolism in Chlamydomonas reinhardtii during induction of CO2-concentrating mechanism: Cellular response to low CO2 stress

Ilka N Abreu,Anna Aksmann,Amit K Bajhaiya,Reyes Benlloch,Mario Giordano,Wojciech Pokora,Eva Selstam,Thomas Moritz

doi:10.1016/j.algal.2020.102099

Abstract

Photosynthetic organisms strictly depend on CO2 availability and the CO2:O2 ratio, as both CO2/O2 compete for catalytic site of Rubisco. Green alga Chlamydomonas reinhardtii, can overcome CO2 shortage by inducing CO2-concentrating mechanism (CCM). Cells transferred to low-CO2 are subjected to light-driven oxidative stress due to decrease in the electron sink. Response to environmental perturbations is mediated to some extent by changes in the lipid and carotenoid metabolism. We thus hypothesize that when cells are challenged with changes in CO2 availability, changes in the lipidome and carotenoids profile occur. These changes expected to be transient, when CCM is activated, CO2 limitation will be substantially ameliorated. In our experiments, cells were transferred from high (5%) to low (air equilibrium) CO2. qPCR analysis of genes related to CCM and lipid metabolism was carried out. Lipidome was analyzed both in whole cells and in isolated lipid droplets. We characterized the changes in polar lipids, fatty acids and ketocarotenoids. In general, polar lipids significantly and transiently increased in lipid droplets during CCM. Similar pattern was observed for xanthophylls, ketocarotenoids and their esters. The data supports our hypothesis about the roles of lipids and carotenoids in tackling the oxidative stress associated with acclimation to sub-saturating CO2.

Highlights

Long and short term carbon (C) and energy budgets of photosynthetic organisms are strongly dependent on CO2:O2 ratios
To test whether the lipid content is modified under limiting CO2 conditions, we measured total lipids from C. reinhardtii cultures grown under high CO2 (H-CO2) or low CO2 (L-CO2) for 3 and 6 h
We did not observe any significant changes in total lipid content after 3 or 6 h of LCO2 treatment compared to High CO2 (H-CO2) (Fig. S3)

Summary

Introduction

Long and short term carbon (C) and energy budgets of photosynthetic organisms are strongly dependent on CO2:O2 ratios. This is due to the fact that CO2 and O2 compete for the active site of ribulose1,5-bisphosphate carboxylase/oxygenase (Rubisco), the enzyme responsible for CO2 fixation. Long term changes in the CO2: O2 ratio have exerted a strong selective pressure on photosynthetic organisms, which, most likely polyphyletically, have acquired mechanisms to pump CO2 into the proximity of Rubisco, the so called CO2 concentrating mechanisms. ⁎ Correspondence to: A.K. Bajhaiya, Algal Biotechnology Lab, Department of Microbiology, School of Life Sciences, Central University of Tamil Nadu, Thiruvarur, Tamil Nadu 610005, India.

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Conclusion