Plant molecular engine out of the chassis: Natural rubber synthesis in cell-free systems

Natural rubber (NR) is one of the most important polymers and is used in more than 40,000 products. The demand for NR is estimated to reach $68.5 billion in 2026. The key commercial source for NR production is the latex of Hevea brasiliensis. However, this tropical plant has limited productivity and a very slow life cycle, is subject to environmental limitations and is susceptible to various pathogens. Thus, the establishment of a cell-free system for NR production is useful. In the current study, we reviewed the majority of significant efforts undertaken over the previous two decades for in vitro NR synthesis using recombinant proteins expressed in bacterial, yeast, plant, and cell-free systems. Furthermore, structural and functional models have been developed for the important concepts to create a solid theoretical baseline for future developments. To date, there is only one successful case in which large cis-polyisoprene chains have been synthesized in vitro by reconstitution of the candidate complex (HRT1-HRBP-REF) on washed rubber particles (WRPs). To develop a complete cell/organelle-free system for NR production, the WRPs were replaced with nanodiscs. The candidate proteins were successfully incorporated into the nanodiscs; however, they could only synthesize small polyisoprene chains. Therefore, further investigations are required to achieve cell-free in vitro NR synthesis.