Comparative proteomics of high light stress in the model alga Chlamydomonas reinhardtii

High light (HL) stress adversely affects growth, productivity and viability of photosynthetic organisms. The green alga Chlamydomonas reinhardtii is a model system to study photosynthesis and light stress. Comparative proteomics of wild-type and two very high light (VHL)-resistant mutants, VHL^R-S4 and VHL^R-S9, revealed complex alterations in response .to excess light. A two-dimensional reference map of the soluble subproteome was constructed representing about 1500 proteins. A total of 83 proteins from various metabolic pathways were identified by peptide mass fingerprinting. Quantitative comparisons of 444 proteins showed 105 significantly changed proteins between wild type and mutants under different light conditions. Commonly, more proteins were decreased than increased, but different proteins were affected in each genotype. Proteins uniquely altered in either VHL ^R mutant may be involved in VHL resistance. Such candidate proteins similarly altered without light stress, thus possibly contributing to "pre-adaptation" of mutants to VHL, included decreased levels of a DEAD box RNA helicase (VHL^R-S4) and NAB1 and RB38 proteins (VHL ^R-S9), and increased levels of an oxygen evolving enhan-cer 1 (OEE1) isoform and an unknown protein (VHL^R-S4). Changes from increased levels in HL to decreased levels in excess light, included OEEl (VHL ^R-S9) or the reverse change for NAB1, RB38, β-carbonic anhydrase and an ABC transporter-like protein (VHL^R-S4).