The identification of novel components of photosynthesis will improve our understanding of this energy generating process and provide us with the foundation needed to engineer plants and algae for increased photosynthetic efficiency, higher agricultural yields and greater tolerance to adverse environmental conditions. Our studies are being guided by an inventory of proteins designated the GreenCut, which is a set of approximately 600 nuclear-encoded proteins conserved among photosynthetic organisms belonging to the Green Lineage (Viridiplantae), but not present (or not highly conserved) in heterotrophic (non-photosynthetic) organisms. Approximately half of the GreenCut proteins have unknown specific functions, with many likely having roles that directly impact photosynthetic activities (electron transport, carbon fixation), the biogenesis of chloroplasts and transcriptional and post-transcriptional processes. We have used biochemical, biophysical and molecular assays to examine photosynthetic processes in several Chlamydomonas reinhardtii mutants that are null for specific GreenCut proteins, including cgl71 and cpld49; these mutants are defective in the assembly of PS I and the cytochrome b6f complex, respectively. We have also begun to explore the roles of various families of GreenCut assembly factors in the biogenesis of photosynthetic complexes and how other GreenCut proteins may be important for sustaining photosynthetic processes under suboptimal nutrient conditions. The results of these studies have mechanistic, regulatory and evolutionary implications.