Illustration of serotonin N-acetyltransferase (SNAT) from the rice plant (Oryza sativa) in complex with acetyl coenzyme A (acetyl-CoA). SNAT, also known as arylalkylamine N-acetyltransferase (AANAT), is the penultimate enzyme in the synthesis of melatonin. It adds the acetyl group from acetyl-coA to a serotonin molecule to form N-Acetylserotonin (NAS). Melatonin regulates plant growth and development processes and stress responses.