Involved in the biosynthesis of hydroxycinnamic acid amides, which play a role in defense against pathogens. Agmatine is the preferred acyl acceptor, lower activity is observed towards putrescine. The preferred acyl donor is p-coumaroyl-CoA, lower activity is seen towards feruloyl-CoA. 4-coumaroyl-CoA + agmatine = CoA + H(+) + N-(4-guanidinobutyl)-4-hydroxycinnamamide Increased susceptibility to A.brassicicola infection. Belongs to the plant acyltransferase family.