Post-transcriptional control of light-harvesting genes expression under light stress.

Plants have to deal with fluctuating light environment and the regulation of the photosynthetic apparatus is crucial for their survival. The large multigenic family of nuclear encoded chloroplastic proteins called light harvesting complex (LHC) is involved in both light harvesting and photoprotection. Changes in light intensity induce a complex set of molecular events within both the chloroplast and the cytoplasmic compartments of the cell leading to reorganization of the photosynthetic apparatus in order to optimize photosynthesis to the new conditions. In this study we have investigated the occurrence of translational regulations during light stress in Arabidopsis thaliana by using polysomes profiling. We have observed a strong effect of light on global translation activity of the cell. We show that individual LHC genes are translationally regulated in response to light conditions by changing the ratio between polysomal versus total messenger RNA. In addition, we found that cytoplasmic translational regulation can precede nuclear transcriptional regulation. Thus translational control appears as an important component of the crosstalk between chloroplast and the nucleus in plant cells.