Light regulation of photosynthetic genes

Light influences plant development at various levels of gene expression. Preferentially photosynthetic genes are light controlled. In the nuclear‐cytosolic compartment this regulation occurs primarily at the level of transcription. To date, the light regulation of chloroplast genes has been observed mainly at the level of translation. However, mainly fully mature chloroplasts have been analyzed and the situation might be different in young chloroplasts, as has been found earlier for nuclear transcription. Finally, regulation also occurs by posttranslational modification. The involvement of the circadian clock in the regulation of gene expression is described in detail. During these studies it has been found that the circadian oscillator influences gene expression at various levels, probably resulting in the coordination of processes which might be harmful to the plant. The synthesis of chlorophylls as well as of their corresponding apoproteins are co‐regulated and reduce dangerous radical formation, especially at the higher light intensities. The maxima of chlorophyll and binding apoproteins occur during the first half of the light phase while other, presumably light‐insensitive processes, are shifted to the dark phase. Under light stress, e.g. full sunlight at 5°C, a different set of genes is activated; these include proteins such as catalases, peroxidases, superoxide dismutase or ELIPs, which are upregulated while the well known ‘light‐in‐ducible genes’ are down‐regulated under light stress conditions.