Translation of psbA mRNA is regulated by light via the 5'-untranslated region in tobacco plastids.

The plastid psbA gene encodes the 32 kDa D1 polypeptide of photosystem II. It has previously been shown that the initiation of psbA mRNA translation in tobacco is regulated by sequences outside of the coding region. To identify the cis-acting regulatory sequences involved in the translational control, a series of chimeric uidA genes, encoding the beta-glucuronidase (GUS) reporter enzyme, were introduced into the plastid genome. GUS accumulation in response to the light (135- to 200-fold), and the arrest of uidA mRNA translation in light-grown seedlings following transfer for 2 h to the dark, was observed only if the transgenes contained the psbA 5'-untranslated leader region (UTR). Changes in GUS accumulation were accompanied by little or no changes in the uidA mRNA levels. The data indicate that the initiation of D1 translation in tobacco plastids is controlled via the psbA 5'-UTR.