Enhancing rubber dandelion germplasm by increasing mevalonate pathway activity

Taraxacum kok-saghyz (TK, a.k.a. rubber dandelion) is a dandelion relative that produces high-quality natural rubber (NR) in its roots. NR is used in about 50,000 products, and while global demand steadily increases, supply is solely dependent on Hevea brasiliensis, the rubber tree. H. brasiliensis is a clonal crop with limited production in South America due to South American Leaf Blight (SALB), making Asia the largest NR producer. Emerging Pestalotiopsis disease in Asia, and possibility of SALB introduction, threatens the world supply of NR. TK could supplement NR production and can be cultivated in the United States but is not economically viable due to low rubber yield. One solution is to improve TK germplasm through biotechnology. The mevalonate (MVA) pathway produces much of the isopentenyl pyrophosphate (IPP) utilized in NR production. Agrobacterium rhizogenes was used to insert a multigene construct containing MVA pathway genes targeted to chloroplasts. The Ri gene co-inserted by A. rhizogenes limits plant growth, but previous work suggests that plants containing the MVA construct and Ri gene overcame the Ri gene’s negative effects on root mass and rubber yield. Ri can usually be confirmed by both PCR and its easily identifiable phenotype. Further studying Ri phenotype in TK could result in selecting plants without Ri without a PCR confirmation, saving time and resources. Breeding TK containing MVA constructs without Ri will enable us to produce plants homozygous for the construct, which may increase IPP pool size and finally NR production, a valuable trait for economically viable TK.