A method of synthesizing sialic acid in plants, and plants capable of synthesizingsialic acid is provided. Furthermore, a method of producing sialylated proteinin a plant is also provided. The method to synthesize sialic acid comprises providinga plant comprising a nucleotide sequence encoding N-acetyl neuraminic acid(Neu5Ac) synthase or Neu5Ac lyase, and expressing the nucleotide sequence therebysynthesizing sialic acid. The plant may also co-express a nucleotide sequenceencoding one or more than one of an epimerase, a CMP-Neu5 Ac synthase, a CMP- Neu5Actransporter and a sialyltransferase.
