Down-Regulation of Small Rubber Particle Protein Expression Affects Integrity of Rubber Particles and Rubber Content in Taraxacum brevicorniculatum

Abstract

The biosynthesis of rubber is thought to take place on the surface of rubber particles in laticifers, highly specialized cells that are present in more than 40 plant families. The small rubber particle protein (SRPP) has been supposed to be involved in rubber biosynthesis, and recently five SRPPs (TbSRPP1–5) were identified in the rubber-producing dandelion species Taraxacum brevicorniculatum. Here, we demonstrate by immunogold labeling that TbSRPPs are localized to rubber particles, and that rubber particles mainly consist of TbSRPP3, 4 and 5 as shown by high-resolution two-dimensional gel electrophoresis and mass spectrometric analysis. We also carried out an RNA-interference approach in transgenic plants to address the function of TbSRPPs in rubber biosynthesis as well as rubber particle morphology and stability. TbSRPP-RNAi transgenic T. brevicorniculatum plants showed a 40–50% reduction in the dry rubber content, but neither the rubber weight average molecular mass nor the polydispersity of the rubber were affected. Although no phenotypical differences to wild-type particles could be observed in vivo, rubber particles from the TbSRPP-RNAi transgenic lines were less stable and tend to rapidly aggregate in expelling latex after wounding of laticifers. Our results prove that TbSRPPs are very crucial for rubber production in T. brevicorniculatum, probably by contributing to a most favourable and stable rubber particle architecture for efficient rubber biosynthesis and eventually storage.

Lipid Droplet-Associated Proteins (LDAPs) Are Required for the Dynamic Regulation of Neutral Lipid Compartmentation in Plant Cells

“…6A). This loss of LD integrity and reduction of LD-associated biochemical activities are similar to results observed for the suppression of SRPPs, which resulted in a destabilization of rubber particles and a reduction in associated polyisoprene biosynthesis (Hillebrand et al, 2012). Furthermore, reduction of oleosin proteins is known to result in aberrant LD formation, organellar instability, and fusions (Siloto et al, 2006;Miquel et al, 2014).…”

The rubber tree genome reveals new insights into rubber production and species adaptation

“…Recent transgenic studies in Taraxacum brevicorniculatum 28,29 also reveal their essential role in rubber biosynthesis. REF and SRPP share a conserved REF motif that is also retained in several stress-related or lipid droplet-associated proteins in plant cells 25,30,31 .…”

A Lettuce (Lactuca sativa) Homolog of Human Nogo-B Receptor Interacts with cis-Prenyltransferase and Is Necessary for Natural Rubber Biosynthesis

“…Their membranes have abundant integral membrane proteins (oleosin in the lipid body and SRPP in the rubber particle) that represent the major components of the membrane proteins. These proteins are known to have structural roles by preventing particle aggregations via charge repulsion (45,46). Although yeast is a heterologous system for NR metabolism, from the observation of localization of CPTL2/ CPT3 on ER in the log phase and on lipid bodies in the stationary phase, this may explain how the ER-synthesized NR is deposited in the rubber particles, analogous to the triacylglycerol deposition in lipid bodies that bud off from the ER (43).…”