Identification of aTaraxacum brevicorniculatumrubber elongation factor protein that is localized on rubber particles and promotes rubber biosynthesis

Summary Two protein families required for rubber biosynthesis in Taraxacum brevicorniculatum have recently been characterized, namely the cis ‐prenyltransferases (Tb CPT s) and the small rubber particle proteins (Tb SRPP s). The latter were shown to be the most abundant proteins on rubber particles, where rubber biosynthesis takes place. Here we identified a protein designated T. brevicorniculatum rubber elongation factor (Tb REF ) by using mass spectrometry to analyze rubber particle proteins. Tb REF is homologous to the Tb SRPP s but has a molecular mass that is atypical for the family. The promoter was shown to be active in laticifers, and the protein itself was localized on the rubber particle surface. In Tb REF ‐silenced plants generated by RNA interference, the rubber content was significantly reduced, correlating with lower Tb CPT protein levels and less Tb CPT activity in the latex. However, the molecular mass of the rubber was not affected by Tb REF silencing. The colloidal stability of rubber particles isolated from Tb REF ‐silenced plants was also unchanged. This was not surprising because Tb REF depletion did not affect the abundance of Tb SRPP s, which are required for rubber particle stability. Our findings suggest that Tb REF is an important component of the rubber biosynthesis machinery in T. brevicorniculatum , and may play a role in rubber particle biogenesis and influence rubber production.