The relationship between EuSRPP1 gene expression and rubber biosynthesis in Eucommia ulmoides Oliver (Du-zhong)

Abstract Because of the unique properties, trans-polyisoprene rubber (TPI) has gradually realized that it has great development potential. Eucommia ulmoides Oliver (E. ulmoides Oliver), also named Du-zhong, is one of the few woody plants producing TPI. The significant expansion of small rubber particle protein and rubber elongation factor (SRPP/REF) genes in E. ulmoides Oliver may be associated with the producing of TPI. To understand the relationship between EuSRPP1 gene expression and rubber biosynthesis in E. ulmoides Oliver, in this study, an overexpression transgenic (OT) vector of EuSRPP1 driven by the act promoter and an RNA interference (RNAi) expression vector of EuSRPP1 were constructed. Then, Agrobacterium-mediated genetic transformation of E. ulmoides Oliver was conducted to obtain the OT and RNAi seedlings. Quantitative Real-time Polymerase Chain Reaction (qRT-PCR) showed that the EuSRPP1 expression levels in OT seedlings significantly increased, and were 2.53 × and 3.68 × higher in OT-1 and OT-2 seedlings, respectively, than the wild-type (WT) seedlings, Meanwhile, the expression levels of E. ulmoides Isopentenyl Diphosphate Isomerase (EuIPPS) and E. ulmoides Farnesyl Diphosphate Synthase (EuFPS) genes in OT plants, which are related to rubber biosynthesis synthesis, were also up-regulated. To the contrary, EuSRPP1 gene expression levels in the RNAi-1 and RNAi-2 seedlings significantly decreased, which were 3.92% and 42.38% of the WT seedlings, respectively. EuIPPS and EuFPS genes expression levels in the RNAi seedlings were also down-regulated. The TPI content analysis revealed that the TPI content in the overexpression EuSRPP1 callus increased to 1.85 × that of the WT callus, whereas that in the RNAi callus decreased to only 52% of the WT callus. Molecular weights of rubber were significantly different in OT callus (2.31 × 106 Da) and RNAi callus (0.36 × 106 Da). Observation of the rubber particles revealed that the rubber particle electron density was higher in OT seedlings, and the immunogold localization results showed that EuSRPP1 was localized to rubber particles. These results indicate that the EuSRPP1 expression level influences the chain elongation, particle development, and content of rubber in E. ulmoides Oliver.