Overexpression of the EuFPS5 gene in Hevea brasiliensis fails to produce Eucommia rubber but affects the biosynthesis of natural rubber

The Eucommia ulmoides rubber (EuR) is a naturally occurring long-chain trans- 1,4-polyisoprene with extensive applications but high production costs. Previous studies suggest that the Eucommia farnesyl diphosphate synthase 5 (EuFPS5) alone is capable of catalyzing the biosynthesis of EuR. As the most high-yielding cis- polyisoprene-producing plant species with a cost-effective latex harvesting system, Hevea brasiliensis exhibits the potential to produce EuR at a lower cost. Via Agrobacterium -mediated transformation, this study generated a transgenic Hevea line overexpressing EuFPS5 (EuFPS5oe). The EuFPS5oe Hevea plants exhibited slightly wrinkled leaves, but no significant difference in growth vigor compared to the wild type control (WT). 1 H and 13 C nuclear magnetic resonance (NMR) analyses indicated that the rubber of 1-year-old EuFPS5oe plants was identical to that of WT, suggesting that EuFPS5 alone is not sufficient to catalyze the biosynthesis of EuR in Hevea . However, compared to the WT, EuFPS5oe plants showed significantly increased rubber content in the leaves, while the rubber molecular weight in the latex decreased. LC-MS/MS analysis showed that the EuFPS5oe latex contained a comparable level of IPP , but a significantly higher level of FPP than the WT. Taken together, our study suggests a role for EuFPS5 in the biosynthesis of FPP in Hevea , provides in vivo evidence that under limited IPP supply, higher FPP level increases rubber production but decreases rubber molecular weight, and thus lays a foundation for future genetic improvement of natural rubber production in Hevea brasiliensis .