Chloroplast, photosystem II, cytochrome b6f complex, posttranscriptional regulation, Arabidopsis, high chlorophyll fluorescence
Chloroplast-localized proteins that are necessary for the biogenesis, performance and acclimation of the photosynthetic protein complexes are currently under intense research. Hundreds of such proteins in the stroma, the thylakoid membrane and the lumen assist the biogenesis and constant repair of the photosynthetic electron transport chain. During recent years forward genetic screens for chloroplast-defective phenotypes have repeatedly led to novel insights into processes involved in the biogenesis of the protein com-plexes of the thylakoid membrane. The identified nuclear-encoded factors are predominantly involved in posttranscriptional processes of chloroplast gene expression. Many proteins are required during chloroplast RNA maturation and stabilization. Pentatrico-peptide repeat (PPR) proteins operate as RNA-binding factors and seem to be the major protein family implicated in functions of chloroplast RNA metabolism. Chloroplast translation is regulated in response to a variety of biotic and abiotic factors, however, only little is known about the molecular mechanisms that underlie these processes. The assembly of the photosynthetic machinery with its numerous cofactors also requires the activity of nuclear-encoded proteins, several of which are conserved throughout the plant kingdom. However, some factors are present only in green alga and higher plants, indicating that the assembly of the photosynthetic apparatus in photosynthetic eukaryotes required the evolution of novel proteins.