Component of the floral volatile benzenoid/phenylpropanoid (FVBP) biosynthetic pathway that controls carbon flux to pigments essential for pollination or UV protection, to numerous pytoalexins synthesized by plants when challenged by pathogens, and to lignins. (E)-cinnamate + O2 + reduced [NADPH--hemoprotein reductase] = (E)-4-coumarate + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] Phenylpropanoid metabolism; trans-4-coumarate biosynthesis; trans-4-coumarate from trans-cinnamate: step 1/1. In corollas, accumulates progressively during flower development, from buds to anthesis, with a peak at flower opening, but fades out in senescing flowers. Repressed by MYB4. Belongs to the cytochrome P450 family.