Abstract
A unicellular green alga Chlamydomonas reinhardtii can acclimate to wide range of CO2 concentrations. It can grow well even at atmospheric level of CO2 by inducing the CO2-concentrating mechanism (CCM). Nine isozymes of extracellular and intracellular carbonic anhydrases (CAs) specifically induced in low-CO2 acclimated cells play key roles in CCM. When CO2 concentration is increased, CCM and CAs is known to disappear. We previously found that the external CA was replaced by an extracellular protein H43/Fea1, indicating cellular high-CO2 response. [Hanawa et al. (2007) Plant Cell Physiol. 48: 299-309]. In this study, we focused to study on high-CO2-inducible extracellular proteins by proteomic analysis using a wall-deficient strain of C. reinhardtii which releases extracellular matrixes to the culture medium. The mass spectrometric analysis on extracellular proteins showed that 22 proteins, including H43/Fea1, among 129 proteins increased their amounts synthesized during acclimation to high-CO2 conditions for 1 d and 3 d. Eleven of those proteins were classified into hydroxyproline-rich glycoprotein groups.
