PII interactions with the acetyl-CoA carboxylase subunits BADC and BCCP co-regulate lipid and nitrogen metabolism in Arabidopsis

Authors: GARNEAU, MATTHEW - Washington State University; JORGE, GABRIEL - University Of Missouri; Shockey, Jay; THELEN, JAY - University Of Missouri; BATES, PHILIP - Washington State University

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2025
Publication Date: 12/5/2025
Citation: Garneau, M.G., Jorge, G.L., Shockey, J.M., Thelen, J.J., Bates, P. 2025. PII interactions with the acetyl-CoA carboxylase subunits BADC and BCCP co-regulate lipid and nitrogen metabolism in Arabidopsis. Plant Physiology. 199(4: Article kiaf627. https://doi.org/10.1093/plphys/kiaf627.
DOI: https://doi.org/10.1093/plphys/kiaf627

Interpretive Summary: The regulation of partitioning of carbon and nitrogen in growing plant cells is extremely complex. Given the fundamental nature of the primary metabolites produced through primary carbon and nitrogen utilizing pathways, cells have evolved multiple layers of regulatory control. While some of these mechanisms have been studied, most are not yet well-understood. Here is presented a deep examination into the interplay between the key enzyme that controls carbon flux into fatty acids and three types of protein interactors that help to control it. Using a series of mutant lines, missing one, two or all three of the key regulators, the changes wrought on carbon and nitrogen metabolism were investigated.

Technical Abstract: In plants the initiation of fatty acid synthesis is catalyzed by acetyl-CoA carboxylase (ACCase) which produces malonyl-CoA. The heteromeric form of ACCase (htACCase) is a holoenzyme consisting of biotin carboxylase and carboxyltransferase sub-complexes, both of which are subject to extensive regulation. Biotin carboxylase activity is controlled in part by the presence of the catalytic biotin carboxyl carrier proteins (BCCP1/2) and/or the non-catalytic, non-biotinylated, biotin/lipoyl attachment domain-containing proteins (BADC1/2/3) that associate with backbone biotin carboxylase (BC) protein. However, the mechanisms regulating BADC and BCCP interaction with BC and thus ACCase activity in planta are not clear. Here we demonstrate the Arabidopsis thaliana regulatory protein PII modulates htACCase activity through independent interactions with BADC and BCCP proteins in a selective manner. Analysis of badc1/2 and badc1/3 mutant lines and the respective pii triple mutants reveal that changes in seed oil and protein accumulation of badc double mutants are PII/nitrogen dependent. Absolute quantification of htACCase subunits and PII in developing seeds suggests that Arabidopsis exerts tight regulation over individual protein stoichiometry to balance oil and protein accumulation. The effects on vegetative and seed development indicate PII and BADC proteins have distinct but overlapping roles in the regulation of plant metabolism.