The present invention relates to a method of producing collagen in a plant or an isolated plant cell comprising expressing in the plant or the isolated plant cell at least one type of a collagen alpha chain and exogenous P4H in a manner enabling accumulation of said at least one type of said collagen alpha chain and said exogenous P4H in a subcellular compartment devoid of endogenous P4H activity, thereby producing the collagen in the plant.