# Biosynthesis of Natural Rubber: Current State and Perspectives
## 3 Omics Analyses Provide New Insights into Natural Rubber Biosynthesis
### Proteome Analysis  
Proteomics is an efficient tool to study the protein abundance and distribution in an organism [115]. Consistent with the genome and transcriptome analyses, proteome analyses also showed that REF/SRPP proteins are the most abundant components in _H. brasiliensis_ latex proteome, while other high or medium-abundance proteins found were more or less different, depending on materials used and protein extraction and treatment/analytic methods [21; 37; 39; 41; 116; 37]. [PERSON] et al. performed proteome analysis of LRPs and SRPs of _H. brasiliensis_ and gave a wealth of information of protein profiles difference between them. Their results revealed that REF (14.7 kDa) was almost equally expressed on both LRPs and SRPs, while REF (19.6 kDa) was highly expressed on LRPs comparedwith SRPs, indicating that different isoforms of REF may play different roles on LRPs and SRPs and the REF (19.6 kDa) might play a termination role in rubber elongation reaction on LRPs [37]. MVA pathway proteins, such as HMGS, were expressed more predominantly on SRPs than on LRPs, which is consistent with the fact that SRPs have higher activity of rubber biosynthesis than LRPs. Signal transduction-related proteins, such as phospholipase D alpha (PLD\(\alpha\)) and ethylene response factor 2 (ERF2), were also expressed at higher levels on SRPs, suggesting the possible involvement of SRPs in the signal transduction of plant hormones or stress responses [37]. Defense and stress-responsive proteins were also a kind of abundant components of the latex proteome. Heat shock cognate 70-kDa protein (HSC70) and eukaryotic translation initiation factor 5A isoform IV (eIF5A-4) had higher expression levels on SRPs, indicating that these proteins may be required for SRPs to maintain homeostasis in regulation of protein quality during rubber biosynthesis and the development of SRPs. HbASRLP1 and HbRLP1 had higher expression levels on LRPs, suggesting that LRPs might be critical in defense or stress-related responses [37]. Besides, higher abundance of \(\beta\)-1,3-glucanase was detected on LRPs than on SRPs, implying that LRPs play more important roles in the latex coagulation mediated by \(\beta\)-1,3-glucanase than SRPs [37]. [PERSON] et al. carried out an in-depth proteome analysis of the _H. brasiliensis_ rubber particles and identified 186 rubber particle proteins [39]. Besides the highly abundant REF/SRPP proteins, many proteins were firstly identified to be on the rubber particles, including the cyclophilin, cytochrome P450, small GTP-binding protein, clathrin, eukaryotic translation initiation factor, annexin, ABC transporter, translationally controlled tumour protein and ubiquitin-conjugating enzymes, which might be involved in rubber biosynthesis, rubber particle biogenesis and other biological processes [39]. Proteome of ethephon or jasmonates-treated _H. brasiliensis_ cultivars and other rubber-producing plants were also investigated. [PERSON] et al. performed the first in-depth comprehensive proteomics analysis of rubber latex following ethylene stimulation and obtained abundant proteins, ethylene responsive latex proteins and differentially expressed phosphoproteins through different analytic methods [117]. They found that ethylene improved the generation of SRPs whereas most genes involved in rubber biosynthesis were inhibited by exogenous ethylene. Their results suggested the improved latex production is probably due to the inhibition of rubber particle aggregation and the resulted prolongation of latex flow [117]. In addition, they also found that post-translational modification and isoform-specific phosphorylation might be important for ethylene-stimulated latex production [117]. [PERSON] et al. treated _H. brasiliensis_ clone Reyan 7-33-97 with ethel and methyl jasmonate (MeJA), respectively, and identified a total of 101 latex proteins that were regulated by ethel and/or MeJA [118].