Essential protein that catalyzes the condensation reaction of fatty acid synthesis by the addition to an acyl acceptor of two carbons from malonyl-ACP. Specific for elongation from C-16 and C-16 to unsaturated C-18 fatty acids. Confers resistance to low temperatures by maintaining chloroplast membranes integrity. Involved in the regulation of fatty acids ratios during seed metabolism. Required for embryo development, especially at the transition from the globular to the heart stage. a fatty acyl-[ACP] + H(+) + malonyl-[ACP] = a 3-oxoacyl-[ACP] + CO2 + holo-[ACP] Homodimer. Mostly expressed in siliques, and, to a lower extent, in leaves, stems, flower buds, and flowers. First observed during the transition from the late globular to the early heart embryo stages. Later observed during heart, tropedo, and cotyledonary embryo stages. In seedlings, observed in the shoot apex and stomatal guard cells. In adult plants, expressed in inflorescences. In flowers, strongly present in styles and pollen grains. Lethal when homozygous due to embryo abortion before the torpedo stage. Converts temperate oilseed composition (rich in unsaturated 18-carbon fatty acids) to that of a palm-like tropical oil (enriched in saturated 16-carbon fatty acids). Belongs to the thiolase-like superfamily. Beta-ketoacyl-ACP synthases family. Truncated N-terminus.