Catalyzes the NADPH-dependent reduction of beta-ketoacyl-ACP substrates to beta-hydroxyacyl-ACP products, the first reductive step in the elongation cycle of fatty acid biosynthesis. a (3R)-hydroxyacyl-[ACP] + NADP(+) = a 3-oxoacyl-[ACP] + H(+) + NADPH Lipid metabolism; fatty acid biosynthesis. Homotetramer. Belongs to the short-chain dehydrogenases/reductases (SDR) family. Extended N-terminus.