Spermidine coumaroyl-CoA acyltransferase that mediates the conversion of spermidine into dicoumaroyl-spermidine. 2 (E)-4-coumaroyl-CoA + spermidine = 2 CoA + 2 H(+) + N(1),N(8)-bis(coumaroyl)-spermidine kcat is 3.4 sec(-1) with coumaroyl-CoA as substrate (in the presence of spermidine as the acyl acceptor). kcat is 3.1 sec(-1) with spermidin as substrate (in the presence of coumaroyl-CoA as the acyl donor). All analyses are done at 30 degrees Celsius. Optimum pH is 9 using spermidine and coumaroyl-CoA as substrates. Amine and polyamine metabolism; spermidine metabolism. Monomer. Mainly expressed in roots at low levels, specifically, in the root tip. Belongs to the plant acyltransferase family.