Multiple Light and Plastid Signals Control Chloroplast Development in Arabidopsis

Abstract

A primary role of chloroplasts is light harvesting, therefore it is not surprising that their development is regulated by the light environment the leaf encounters. In angiosperms, different aspects of chloroplast development are regulated at two major stages. Firstly, chloroplasts do not develop in the dark. Light perception is required for the completion of chlorophyll biosynthesis, and for the expression of a large number of nuclear and some chloroplast-encoded photosynthetic genes. This “greening” is part of the de-etiolation process of newly germinated seedlings, triggered by light activation of phytochromes (1). Secondly, the balance between components involved in photochemical and in non-photochemical reactions appears to be optimised for light harvesting under shade light, and for carbon fixation and the prevention of photoinhibition under sun light (2). The phenomenon is known as photosynthetic acclimation. In addition to the light control, signals of plastid origin have been proposed, which exert overall control on the expression of photosynthetic genes (3,4) or modulate it in acclimation (5). We are seeking to contribute to the understanding of both types of light signals, and how they may related to the proposed plastid-originated signals, using a combined genetic and molecular-physiological approach in the model species Arabidopsis thaliana.