Active on both saturated and mono-unsaturated acyl chains C16 to C20. a very-long-chain acyl-CoA + H(+) + malonyl-CoA = a very-long-chain 3-oxoacyl-CoA + CO2 + CoA Lipid metabolism; fatty acid biosynthesis. Only expressed in guard cells. Expressed in siliques, flowers, leaves, stems, roots and seedlings (PubMed:18465198). Repressed by herbicides such as flufenacet and benfuresate (PubMed:12916765). Down-regulated by darkness and low temperature (PubMed:18465198). Belongs to the thiolase-like superfamily. Chalcone/stilbene synthases family.