Acclimation to low CO2 concentrations in the green alga Chlamydomonas reinhardtii. A sub-organellar phosphoproteomic survey of the potential transduction pathways

Amaya Blanco-Rivero1,3, Flor Martínez1, Maria Turkina2, Alexander Vener2, Göran Samuelsson3 and Arsenio Villarejo1,3

1Dept. of Biology, Universidad Autónoma de Madrid, Madrid 28049, Spain 2Division of Cell Biology, University of Linköping, 58185 Linköping, Sweden 3,1Umeå Plant Science Centre, Dept. of Plant Physiology, Umeå University, Umeå, Sweden

Phosphorylation of thylakoid membrane proteins has been implicated in adaptive responses to environmental stress factors, including nutrient limitation. Green algae induce a CO2-concentrating mechanism (CCM) when growing under low CO2 concentrations in the medium. CCM allows algal cells to elevate the CO2 concentration at the active site of Rubisco, ensuring efficient photosynthesis even under CO2 limiting conditions. Although the CCM has been extensively studied, little is known about the way algal cell senses changes in the CO2 levels in the environment and the pathways by which this signal is transduced to the nucleus. We have performed a mass spectrometry-based analysis of the in vivo thylakoid protein phosphorylation events taking place in response to CO2 limitation in Chlamydomonas reinhardtii. We have identified a low-CO2-inducible protein, Lci5, which is peripherally associated with the stromal side of the thylakoids from cells growing under both high and low CO2 conditions. Lci5 is accumulated and become phosphorylated in the early steps of acclimation to low CO2 conditions. The transcript for the protein is rapidly accumulated within the first 2 h under limiting CO2 conditions and then declined steadily afterwards, suggesting that Lci5 may be involved in the primary sensing events controlling the induction of the CCM. In order to characterize the specific function of Lci5, we have carried out an in-depth analysis of Lci5 localization, protein-crosslinking studies and RNAi gene silencing. Results will be presented in this conference.

e-mail address of presenting author: amaya.blanco@uam.es