ADP-dependent phosphorylation regulates RNA-binding in vitro: implications in light-modulated translation

Area of Science:

• Plant molecular biology
• Chloroplast gene expression
• Photosynthesis research

Background:

• Nuclear factors regulate light-dependent translation of chloroplast mRNAs in Chlamydomonas reinhardtii.
• These factors bind the 5 acronym{'-untranslated region (5 acronym{'-UTR) of specific mRNAs, enhancing translation.
• Proteins binding the psbA mRNA 5 acronym{'-UTR were previously identified, with binding activity increasing in light.

Purpose of the Study:

• To investigate the mechanism of light-regulated translation of psbA mRNA.
• To identify factors involved in the inactivation of psbA mRNA binding.
• To elucidate the role of ADP in regulating chloroplast mRNA translation.

Main Methods:

• Identification of a serine/threonine protein phosphotransferase within the psbA mRNA-binding complex.
• In vitro phosphorylation assays using ADP to inactivate mRNA binding.
• Correlation of in vivo ADP levels with chloroplast mRNA translation regulation.

Main Results:

• A serine/threonine protein phosphotransferase uses ADP to phosphorylate and inactivate psbA mRNA binding in vitro.
• In vitro inactivation is triggered by high ADP concentrations.
• High ADP levels occur in vivo in dark-grown chloroplasts.

Conclusions:

• Chloroplast psbA mRNA translation is attenuated by phosphorylation of the mRNA-binding protein complex.
• This phosphorylation is induced by increased stromal ADP levels upon transfer to darkness.
• The findings reveal a novel regulatory mechanism for chloroplast gene expression in response to light changes.