Enhancement of the plastidic acetyl-CoA carboxylase level using the tobacco plastid transformation

Abstract

The plastidic acetyl-CoA carboxylase (ACCase) catalyzes the formation of malonyl-CoA for the de novo fatty acid biosynthesis. This is a fundamental process required for the oil production. In most plants, this enzyme is a heteromeric complex composed of four different polypeptides: biotin carboxylase (BC), biotin carboxyl carrier protein (BCCP), and the alpha and beta subunits of carboxyltransferase (CT-alpha and CT-beta). Among the four polypeptides, CT-beta is encoded in chloroplast genome. To increase oil content in tobacco seeds, we examined to enhance the plastidic ACCase level by modifying plastid gene expression. The accD gene encoding CT-beta is exclusively transcribed by NEP (nuclear-encoded RNA polymerase) and its mRNA level is low. The accD gene promoter was replaced with the rrn (ribosomal RNA operon) 16 promoter using the tobacco plastid transformation. The replaced promoter is recognized by NEP and PEP (plastid-encoded RNA polymerase). We have obtained several transformants. The accD mRNA and CT-beta protein levels in the transformants were significantly greater than the wild-type levels. We will report the effect of altered CT-beta level on the other subunit levels and the oil production