Acetyl-CoA carboxylase catalyzes the formation of malonyl-CoA from acetyl-CoA. The four genes encoding heteromeric acetyl-CoA carboxylase are coordinately expressed in leaves, flowers, and developing siliques and embryos. The highest expression occurs in tissues undergoing rapid growth and high oil deposition. The gene encoding the E1 [beta] subunit of chloroplastidic pyruvate dehydrogenase has an identical pattern, indicating it may provide acetyl-CoA for seeds. In contrast, the gene encoding acetyl-CoA synthetase has a different expression pattern and is expressed at low levels in seeds;The ACC1 genes encoding homomeric acetyl-CoA shows transient expression in a variety of cell types. The homomeric acetyl-CoA carboxylase mRNA accumulates to high levels in the epidermis of a variety of organs at the time of expansion. The highest accumulation occurs in the inner integuments of ovules at the time of testa deposition, the tapetum, the stigma and ovules of the flower buds, and trichomes. The expression pattern of this single gene may reflect the diverse requirements of cytosolic malonyl-CoA for synthesis of phytochemicals such as cuticular waxes, anthocyanins, stilbenoids, phlobaphens, and malonated aminocyclopropane-1-carboxylic acid. The expression pattern of the citrate lyase gene is almost identical, indicating this enzyme may provide cytosolic acetyl-CoA for homomeric acetyl-CoA carboxylase;Biotin (vitamin H) is the cofactor required for the activity of acetyl-CoA carboxylase and other carboxylases and decarboxylases. Biotin synthase catalyzes the last step of biotin synthesis. The gene encoding biotin synthase is highly expressed in young leaves, trichomes, young buds and the epidermis of young stems. The biotin synthase mRNA starts to accumulate in the epidermis of siliques only 3-4 days after flowering, and remains at a high level in 13 day-old siliques, which have started to become yellow and in which the expression of many other genes has shut down. In the embryos, the pattern of biotin synthase RNA is very similar to that of heteromeric acetyl-CoA carboxylase mRNAs, probably in part due to the biotin required for acetyl-CoA carboxylase activity at this time
