METHOD FOR PRODUCING NATURAL RUBBER， TRANSGENIC PLANT， METHOD FOR PRODUCING PNEUMATIC TIRE， AND METHOD FOR PRODUCING RUBBER PRODUCT

To provide methods for producing a natural rubber which enable the production of a natural rubber with an increased molecular weight， and transgenic plants which are able to produce a natural rubber with an increased molecular weight. Included is a method for producing a natural rubber， the method including the steps of: introducing a gene coding for a cis-prenyltransferase (CPT) family protein derived from a rubber-producing plant A into a rubber-producing plant B to prepare a transgenic plant C; and producing a natural rubber using the transgenic plant C， the rubber-producing plant A producing a natural rubber having a higher molecular weight than a natural rubber produced by the rubber-producing plant B not transfected with the gene.