This invention pertains to nucleic acid fragments encoding plant cis-prenyltransferases. More specifically, this invention pertains to a cis-prenyltransferase homolog from latex of the rubber-producing plant species Taraxacum kok-saghyz (russian dandelion) and a cis-prenyltransferase homolog from the rubber-producing plant species Helianthus annus (sunflower).