Involved in the latter stages of lignin biosynthesis. Catalyzes one of the last steps of monolignol biosynthesis, the conversion of cinnamoyl-CoAs into their corresponding cinnamaldehydes. Probably involved in the formation of lignin in defense responses. (E)-cinnamaldehyde + CoA + NADP(+) = (E)-cinnamoyl-CoA + H(+) + NADPH Activated by the small GTPase RAC1. Aromatic compound metabolism; phenylpropanoid biosynthesis. Interacts with RAC1 in a GTP-dependent manner. By sphingolipid elicitor (SE). Belongs to the NAD(P)-dependent epimerase/dehydratase family. Dihydroflavonol-4-reductase subfamily.