Spatio temporal expression of nuclear encoded proteins associated to the plastid encoded RNA polymerase essential for chloroplast biogenesis in Arabidopsis thaliana L. The development of functional chloroplasts originating from undifferentiated proplastids is a complex process that depends on the proper function of the plastid encoded RNA polymerase (PEP). The PEP complex comprises the plastid encoded bacteria like core proteins αββ ʹβʺ and 12 tightly associated nuclear encoded proteins (PAPs; Steiner et al. 2011; Pfalz and Pfannschmidt 2013). Biochemical analyses suggest expression and assembly of these proteins appears in a development and or light dependent manner however this process is far from understood. It however represents a bottleneck in chloroplast biogenesis since genetic inactivation of any PAP disturbs the plastid gene expression resulting in an ivory albino mutant phenotype. This thesis provides a detailed catalogue of the temporal and spatial expression of PAP genes during seedling development and describes novel and unexpected features of PAP localization particularly with regard to the dual distribution between nucleus and plastid. Future studies will target mechanisms that control this dual localization and will aim to identify a transcriptional master regulator of the PAPs. The reporter lines that were designed during this thesis will provide useful tools for the assessment of these open questions.