Polyribosome loading of spinach mRNAs for photosystem I subunits is controlled by photosynthetic electron transport.

In light-, but not in dark-grown spinach seedlings, the mRNAs for the nuclear-encoded photosystem I subunits D, F and L are associated with polyribosomes and this association is prevented by the application of 3-(3',4'-dichlorophenyl)-1,1'-dimethyl urea (DCMU), an inhibitor of the photosynthetic electron transport. To identify the cis-elements which are responsible for this regulation, we generated a series of chimeric PsaD constructs and tested them in transgenic tobacco. The spinach PsaD 5'-untranslated region is sufficient to confer light- and photosynthesis-dependent polyribosome association onto the uidA reporter gene, while the tobacco PsaD 5'-untranslated region directs constitutive polyribosome association. These results are discussed with regard to signals from photosynthetic electron flow which control processes in the cytoplasm.