The Comparative Proteomic Studies On The Regulation Of Rubber Particle Proteins On Natural Rubber Biosynthesis In Rubber Tree

Rubber particle (RP) is an organelle for the biosynthesis and storage of natural rubber. Proteins associated with rubber particle membrane are mainly involved in rubber biosynthesis. It has been traditionally believed that the biosynthesis of isoprene pyrophosphate ester (IPP), the direct precursor of natural rubber occurred in cytoplasm (C-serum) whereas, rubber particle bear the extension of rubber hydrocarbon molecules. That means the site of biosynthesis of precursor is completely separate from the site of the extension of rubber hydrocarbon molecules in laticifers. Recent evidence including our primary results show that enzymes for the regulation of the biosynthesis of precursors of natural rubber which have been believed to be present in serum are found to be located on the membrane of rubber particle, suggesting that the biosynthesis of precursors of natural rubber is also underway on the membrane of rubber particle. In the present study, latex samples were collected from8-year-old virgin trees of rubber tree clone Reyan7-33-97. Rubber particles were separated by high-speed centrifugation of the collected fresh latex samples, followed by percoll gradient centrifugation to obtain the samples of small rubber particles and large rubber particles. The separated rubber particle samples were washed by the traditional method, and the components in the washing buffer and washed rubber particles were collected respectively. Protens in the collected samples were extracted by BPP method for the purpose of comparative proteomic analysis. The results as follows:1. Lots of proteins associated with rubber particles were easy to be lost during mild but time-cost washing, the method for traditionally washing rubber particles.2. Mevalonate kinase, a key enzyme for the biosynthesis of precursor of natural rubber, were detected by Western-blot in the washing buffer of rubber particles.3. Both small rubber particle protein (SRPP) and rubber elongation factor (REF) went through several post-translational modification, which may be essential for the regulation of natural rubber biosynthesis.4. The level of26S proteasome, which was in charge of the degradation of ubiqitin-tagged proteins, in large rubber particles was higher than that in small rubber particles.The results highlight the role of rubber particles in the regulation of natural rubber biosynthesis. They may be directly involved in whole process from precursor biosynthesis to rubber hydrocarbon molecules. And moreover, functions of small rubber particles and large rubber particles may be different in the regulation of initiation and termination of natural rubber biosynthesis.