Arabidopsis acyl carrier protein4 and rhomboid like10 act independently in chloroplast phosphatidate synthesis

Authors: XU, YANG - Michigan State University; KAMBHAMPATI, SHRIKAAR - Donald Danforth Plant Science Center; Morley, Stewart; COOK, RON - Michigan State University; FROEHLICH, JOHN - Michigan State University; Allen, Douglas - Doug; BENNING, CHRISTOPH - Michigan State University

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/18/2023
Publication Date: 9/2/2023
Citation: Xu, Y., Kambhampati, S., Morley, S.A., Cook, R., Froehlich, J., Allen, D.K., Benning, C. 2023. Arabidopsis acyl carrier protein4 and rhomboid like10 act independently in chloroplast phosphatidate synthesis. Plant Physiology. 193(4): 2661-2676. https://doi.org/10.1093/plphys/kiad483.
DOI: https://doi.org/10.1093/plphys/kiad483

Interpretive Summary: In plant cells, lipids can be produced using similar biochemical pathways but involving different substrates and taking place in one of several subcellular locations. The generation of lipids is necessary to form membranes that segregate compartments within a cell that enable it to function correctly for plant growth. In addition, lipids are energy dense and understanding lipid production can be important for the production of biofuels that are an important part of a sustainable economy. In the current studies, mutants in one of the lipid biosynthetic pathways were used to study lipid production. The investigations included measurement of lipids and metabolites involved in lipid biosynthesis. The studies identified important roles for genes involved in lipid pathways and that affect the final lipid composition. Such studies are important because they contribute to our understanding of plant cellular lipid metabolism and provide inspiration for how plants might be rationally engineered to augment biomass and in particular lipid profiles.

Technical Abstract: ACYL CARRIER PROTEIN4 (ACP4) is the most abundant ACP isoform in Arabidopsis (Arabidopsis thaliana) leaves and acts as a scaffold for de novo fatty acid biosynthesis and as a substrate for acyl-ACP-utilizing enzymes. Recently, ACP4 was found to interact with a protein-designated plastid RHOMBOID LIKE10 (RBL10) that affects chloroplast monogalactosyldiacylglycerol (MGDG) biosynthesis, but the cellular function of this interaction remains to be explored. Here, we generated and characterized acp4 rbl10 double mutants to explore whether ACP4 and RBL10 directly interact in influencing chloroplast lipid metabolism. Alterations in the content and molecular species of chloroplast lipids such as MGDG and phosphatidylglycerol were observed in the acp4 and rbl10 mutants, which are likely associated with the changes in the size and profiles of diacylglycerol (DAG), phosphatidic acid (PA), and acyl-ACP precursor pools. ACP4 contributed to the size and profile of the acyl-ACP pool and interacted with acyl-ACP-utilizing enzymes, as expected for its role in fatty acid biosynthesis and chloroplast lipid assembly. RBL10 appeared to be involved in the conversion of PA to DAG precursors for MGDG biosynthesis as evidenced by the increased 34:x PA and decreased 34:x DAG in the rbl10 mutant and the slow turnover of radiolabeled PA in isolated chloroplasts fed with [14C] acetate. Interestingly, the impaired PA turnover in rbl10 was partially reversed in the acp4 rbl10 double mutant. Collectively, this study shows that ACP4 and RBL10 affect chloroplast lipid biosynthesis by modulating substrate precursor pools and appear to act independently.