Establishment of photosynthesis through chloroplast development is controlled by two distinct regulatory phases. Establishment of photosynthesis through chloroplast development is controlled by two distinct regulatory phases

A pluripotent inducible cell line was generated from Arabidopsis to address the limitations of traditional in planta dicot systems and to develop a well-controlled experimental setup where the individual regulatory check points of chloroplast development could be defined. Following light exposure, this cell line was shown to differentiate into photosynthetically active cells with functional chloroplasts providing an experimental system with a temporal gradient of chloroplast development. Using this unique cell line from the dicot Arabidopsis we could demonstrate that the development from a proplastid to a functional chloroplast, and thereby the establishment of photosynthesis, is dependent on a regulatory mechanism involving two distinct phases. First, light exposure triggers an initial change in gene expression, metabolite profile, chlorophyll accumulation and plastid structure. Secondly, a second signal, most likely triggered by activation of the chloroplast, is required for full transition to a functional chloroplast and the shift from heterotrophic to photoautotrophic metabolism.