Expression of the genes coding for plastidic acetyl-CoA carboxylase subunits is regulated by a location-sensitive transcription factor binding site.

Plastidic acetyl-CoA carboxylase (ACCase) regulates the rate of fatty acid synthesis. This enzyme is composed of biotin carboxyl carrier protein (BCCP), biotin carboxylase (BC), and carboxyltransferase (CT), which consists of α and β subunits. Among these components, CTβ is encoded by the plastidic genome. In Arabidopsis, BC and CTα are each encoded by a single gene, and there are two genes for BCCP, BCCP1 and BCCP2. Promoter analysis revealed that the 5'-UTR containing the AW box is necessary for the expression of these genes in seeds and seedlings. The results indicated that there are other transcription factors besides WRI1 that bind to the AW box and regulate these genes in organs other than seeds. Although the AW boxes at 748 and 532 bp upstream from the transcription start sites (TSSs) of the BC and CTα genes, respectively, were not functional in seeds, the latter was functional in seedlings. In addition, when these AW boxes were moved to approximately 200 bp upstream from the TSS, they became active in seeds but not in seedlings. These results suggest that the distance from the TSS affects the function of the AW box, and the AW box alone is not sufficient for expression in seedlings. A comparison of the protein levels of BC, BCCP1, BCCP2 and CTβ between a wri1 mutant, a WRI1-overexpressing line and control plants showed that protein levels of BCCP2 and BC but not BCCP1 and CTβ are affected by WRI1. The results suggest that ACCase subunits are differentially regulated by WRI1.