Catalyzes all the condensation reaction of fatty acid synthesis by the addition to an acyl acceptor of two carbons from malonyl-ACP. Able to elongate saturated acyl chains from 4 to at least 16 carbons. Uses malonyl-CoA but not acetyl-CoA as primer substrate. When expressed in a heterologous system, reveals a bimodal distribution of products, with peaks at C8 and C14-C16. The major product of the reaction (octanoyl-ACP) is required for the lipoylation of essential mitochondrial proteins. a fatty acyl-[ACP] + H(+) + malonyl-[ACP] = a 3-oxoacyl-[ACP] + CO2 + holo-[ACP] Inhibited by cerulenin. Lipid metabolism; fatty acid biosynthesis. Homodimer. Expressed at the same level in leaves, roots and flowers. Slow growth and bleached leaf phenotype when grown under ambient air, but normal growth under CO(2)-enriched air. Highly prevents lipoylation of the H-protein subunit of the glycine decarboxylase (GDC) in leaves, but has only a limited effect on the lipoylation of the E2 subunits of pyruvate dehydrogenase (PDH) and alpha-ketoacid dehydrogenase (KGDH) complexes in leaves and even no effect in roots. Mitochondrial protein lipoylation in leaves does not exclusively depend on the lipoate biosynthesis by KAS and may occur independently of this pathway in roots. Belongs to the thiolase-like superfamily. Beta-ketoacyl-ACP synthases family.