Mitochondrial Fatty Acid Synthase Utilizes Multiple Acyl Carrier Protein Isoforms

Acyl carrier protein (ACP) is a highly conserved cofactor protein that is required by Type II fatty acid synthases (FASs). Here, we demonstrate that up to three mitochondrial ACP (mtACP) isoforms support the Arabidopsis () mitochondrially localized Type II FAS. The physiological importance of the three mtACPs was evaluated by characterizing the single, double, and triple mutants. The (At2g44620), (At1g65290), and (At5g47630) single mutants showed no discernible morphological growth phenotype. Functional redundancy among the three mtACPs was indicated by the embryo-lethal phenotype associated with simultaneous loss of all three genes. Characterization of all double mutant combinations revealed that although the and double mutant combinations showed no observable growth defect, the double mutant was viable but displayed delayed growth, reduced levels of posttranslationally lipoylated mitochondrial proteins, hyperaccumulation of photorespiratory Gly, and reduced accumulation of many intermediates in central metabolism. These alterations were partially reversed when the double mutant plants were grown in a nonphotorespiratory condition (i.e. 1% CO atmosphere) or in the presence of 2% Suc. In summary, mtACP, as a key component of mitochondrial fatty acid biosynthesis, is important in generating the fatty acid precursor of lipoic acid biosynthesis. Thus, the incomplete lipoylation of mitochondrial proteins in mutants, particularly Gly decarboxylase, affects the recovery of photorespiratory carbon, and this appears to be critical during embryogenesis.