Biology Department Seminar

Photosystem II (PSII) is the protein-pigment complex in oxygenic photosynthesis that uses light energy to catalyze the oxidation of water. How the subunits and cofactors that make up this enzyme are properly assembled into a functional photosystem remains unknown. To uncover new components in this process, I undertook a chlorophyll fluorescence-based mutant screen in the unicellular green alga Chlamydomonas reinhardtii. One isolated mutant had no detectable PSII activity, whereas other components of the photosynthetic electron transport chain were still functional. This defect was shown to be due specifically to the absence of a gene, RBD1, encoding a thylakoid membrane-bound iron-sulfur protein known as a rubredoxin. Examination of cyanobacterial (Synechocystis) and plant (Arabidopsis) mutants lacking the homolog of RBD1 revealed PSII-specific phenotypes, supporting the hypothesis that this rubredoxin has a conserved role in PSII-containing organisms. The phylogenetic profile of the RBD1 gene led us to hypothesize that other genes involved in PSII assembly or function might show a similar phylogenetic distribution. We devised a computational approach to find these genes and preliminary results indicate that some genes found through this method might indeed be associated with PSII function or assembly.