Plant acetyl-CoA carboxylase: The homomeric form and the heteromeric form

• Can the plant starch-lipid interplay be exploited for increasing TAG production in plants. • Plastid acetyl-CoA carboxylase's multi-subunit structure makes it a complex enzyme to study. • A membrane-protein family negatively regulates plastid acetyl-CoA carboxylase. • Plastid α-carboxyltransferase contains a highly acidic hotspot for phosphorylation. Across the domains of life, the enzyme acetyl-CoA carboxylase (ACC) converts HCO 3 − , ATP, and acetyl-CoA to malonyl-CoA, ADP, and P i . Malonyl-CoA is the building block for all de novo fatty acid biosynthesis. ACC is found in two forms, (1) as a heteromeric enzyme, and (2) as a homomeric enzyme. Whether a single polypeptide, or various subunit combinations, they all catalyze the ATP-dependent carboxylation of acetyl-CoA to form malonyl-CoA. Here, we explore five burning questions pertaining to this fascinatingly intricate and complicated molecular machine, and the prospect of increasing oil production in plant vegetative tissues through its manipulation. We ask: 1. Can we manipulate the interplay of starch-lipid biosynthesis to increase the total TAG content in the vegetative tissues of plants? 2. Why is ACC such a complex enzyme? 3. How is ACC regulated? 4. Why is the plant plastid ACC recruited to the chloroplast membrane? 5. Will structural biology provide insights into the regulation of plant ACC?