In recent years there has been extensive experimental evidence indicating that the nuclear expression of certain genes , in particular those that encode chloroplast proteins is subject to regulation by signals of retrograde plastid origin . This can be done both at the level of transcription and translation of mRNA . Certain plastid origin signals could be identified - these include metabolic precursor of chlorophyll plastochinonu redox state , thioredoxin and glutathione and phosphoenolpyruvate translocator located in the chloroplast inner envelope membrane .