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Natural rubber is a kind of indispensable biopolymers with great use and strategic importance in human society. However, its production relies almost exclusively on rubber-producing plants Hevea brasiliensis, which have high requirements for growth conditions, and the mechanism of natural rubber biosynthesis remains largely unknown. In the past two decades, details of the rubber chain polymerization and proteins involved in natural rubber biosynthesis have been investigated intensively. Meanwhile, omics and other advanced biotechnologies bring new insight into rubber production and development of new rubber-producing plants. This review summarizes the achievements of the past two decades in understanding the biosynthesis of natural rubber, especially the massive information obtained from the omics analyses. Possibilities of natural rubber biosynthesis in vitro or in genetically engineered microorganisms are also discussed.

Enhanced natural rubber biosynthesis is associated with the activation of the COI1-JAZ3-MYC2 jasmonate signalling module in laticifer cells of rubber trees. Abstract Rubber trees are the world's major source of natural rubber. Rubber-containing latex is obtained from the laticifer cells of the rubber tree (Hevea brasiliensis) via regular tapping. Rubber biosynthesis is a typical isoprenoid metabolic process in the laticifer cells; however, little is known about the positive feedback regulation caused by the loss of latex that occurs through tapping. In this study, we demonstrate the crucial role of jasmonate signalling in this feedback regulation. The endogenous levels of jasmonate, the expression levels of rubber biosynthesis-related genes, and the efficiency of in vitro rubber biosynthesis were found to be significantly higher in laticifer cells of regularly tapped trees than those of virgin (i.e. untapped) trees. Application of methyl jasmonate had similar effects to latex harvesting in up-regulating the rubber biosynthesis-related genes and enhancing rubber biosynthesis. The specific jasmonate signalling module in laticifer cells was identified as COI1-JAZ3-MYC2. Its activation was associated with enhanced rubber biosynthesis via up-regulation of the expression of a farnesyl pyrophosphate synthase gene and a small rubber particle protein gene. The increase in the corresponding proteins, especially that of farnesyl pyrophosphate synthase, probably contributes to the increased efficiency of rubber biosynthesis. To our knowledge, this is the first study to reveal a jasmonate signalling pathway in the regulation of rubber biosynthesis in laticifer cells. The identification of the specific jasmonate signalling module in the laticifer cells of the rubber tree may provide a basis for genetic improvement of rubber yield potential.

Rubber elongation factor (REF) and small rubber particle protein (SRPP) are critical components in the biosynthesis of natural rubber in Hevea species, with both proteins playing significant roles in regulating stress responses. Despite recent advancements in understanding their regulatory mechanisms, a comprehensive analysis of their functional roles, gene evolution, expression patterns, and biological regulation is still needed. This review consolidates current knowledge on REF and SRPP, highlighting their evolutionary history and the influence of environmental factors and hormonal signals on their transcriptional regulation. Additionally, it explores the potential of REF and SRPP in plant breeding, not only for improving rubber-producing plants but also for enhancing stress tolerance in non-rubber-producing species. The review emphasizes the need for further research into the molecular mechanisms driving REF and SRPP function, including their involvement in stress resilience and interactions with other proteins in rubber biosynthesis. By synthesizing the latest findings, this work aims to inform future breeding strategies and genetic engineering efforts, with a particular focus on improving rubber production efficiency and increasing plant resistance to abiotic stresses such as drought and salinity. This review provides valuable insights for optimizing the utilization of REF and SRPP in future crop improvement programs. Key message This review highlights the critical role of REF and SRPP in natural rubber biosynthesis and plant adaptation to abiotic stress. The complex evolutionary divergence of REF and SRPP underscores the need for deeper investigation into their mechanisms of action. Further exploration of their functions and applications offers exciting opportunities to uncover novel insights into the molecular pathways driving natural rubber biosynthesis and stress responses in plants. With advancements in transgenic technologies and molecular breeding, REF and SRPP are poised to play a transformative role in developing improved rubber-producing plant varieties and significantly enhancing plant resilience to abiotic stresses.

Plants belonging to the genus Taraxacum are widespread all over the world, which contain rubber-producing and non-rubber-producing species. However, the genomic basis underlying natural rubber (NR) biosynthesis still needs more investigation. Here, we presented high-quality genome assemblies of rubber-producing T. kok-saghyz TK1151 and non-rubber-producing T. mongolicum TM5. Comparative analyses uncovered a large number of genetic variations, including inversions, translocations, presence/absence variations, as well as considerable protein divergences between the two species. Two gene duplication events were found in these two Taraxacum species, including one common ancestral whole-genome triplication and one subsequent round of gene amplification. In genomes of both TK1151 and TM5, we identified the genes encoding for each step in the NR biosynthesis pathway and found that the SRPP and CPT gene families have experienced a more obvious expansion in TK1151 compared to TM5. This study will have large-ranging implications for the mechanism of NR biosynthesis and genetic improvement of NR-producing crops.

[This corrects the article DOI: 10.3389/fpls.2025.1655155.].

Background Tapping panel dryness (TPD) in rubber tree has become the most severe restricting factor of natural rubber production. To date, there is no effective measures to prevent and control TPD. Previous studies primarily focused on analyzing the molecular mechanism underlying TPD occurrence. However, there is no research on the molecular mechanism of TPD recovery. Results In this study, the TPD trees were recovered by treatment with TPD rehabilitation nutrient agents that could promote the recovery of latex flow on the tapping panel of TPD trees. The genes and proteins involved in TPD recovery were first identified by employing integrated transcriptomics and proteomics analyses. In total, 2029 differentially expressed genes (DEGs) and 951 differentially expressed proteins (DEPs) were detected in the bark of recovery trees compared to that of TPD trees. Among them, 19 DEPs and 11 DEGs were found to be involved in the starch and sucrose metabolism pathway, suggesting their important roles in regulating the syntheses of sucrose and D-glucose, which were the key precursors of natural rubber biosynthesis. Furthermore, 16 DEPs and 15 DEGs were identified in the rubber biosynthesis pathway. Interestingly, almost all the DEPs and DEGs related to rubber biosynthesis exhibited significantly up-regulated expressions in the recovery trees, indicating that latex biosynthesis were probably markedly enhanced during TPD recovery. Conclusions These results provide new insights into the molecular mechanisms underlying TPD recovery, as well as excellent supplements to the mechanisms of TPD occurrence, which will contribute to the development of more effective agents for the prevention and treatment of TPD in the future.

The increase in demand for natural rubber has led to the search for alternative sources. Lactuca serriola is emerging as a promising candidate, as the quality of the natural rubber it produces is comparable to that of the Pará Rubber Plant, Hevea brasiliensis . This study examines the effect of methyl jasmonate (MeJA), a known elicitor, on the expression of key rubber biosynthesis pathway genes ( HMGR1 , HMGS1 , CPT2 , and SRPP1 ) in the latex of L. serriola plants. The expression levels of these genes increased significantly after the foliar application of 200 and 400 µM MeJA. The highest relative expression level for HMGR1 , HMGS1 , CPT2 and SRPP1 was 3.74, 18.56, 11.91and 16.59 fold respectively. Furthermore, the rubber content in L. serriola showed a significant rise post-treatment compared to the control with increasing the level of MeJA (6.19%, 7.24% and 7.85% which correspond to 0, 200 and 400 µM). Gel permeation chromatography revealed an augmentation in the molecular weight of extracted natural rubber from treated plants. Samples treated with 400 µM of MeJA had the highest molecular weight (1570 kg mol −1 ) compared to control (1186 kg mol −1 ). This study has demonstrated that MeJA, through the regulation of rubber biosynthesis genes, is capable of enhancing the quality and quantity of natural rubber extracted from alternative sources, such as L. serriola .

Cytochrome P450 monooxygenases (CYPs) are crucial in plant secondary metabolism, catalyzing diverse biochemical reactions, defense, and stress adaptation. Hevea brasiliensis is the primary source of natural rubber, but its CYP family remains underexplored, which may play essential roles in rubber biosynthesis and environmental tolerance. n this study, we systematically identified 238 HbCYP genes in H. brasiliensis, classified them into 9 clans and 43 subfamilies, with Clan 71 contraction and Clan 72 and Clan 85 emerging as the most expansive clans. Gene structure analysis revealed that 68.87% of A-type HbCYPs have one intron. Separately, analysis of conserved motifs in promoter regions identified a high abundance of cis-acting elements, including 456 related to methyl jasmonate (meJA) responsiveness and 3,302 related to light responsiveness. Genome evolution analysis indicated that 64 tandem and 119 WGD or segmental duplications significantly contributed to the expansion of the HbCYP family, also supported by orthologous genes with other four species. Tissue-specific profiling revealed differential HbCYPs expression across H. brasiliensis organs. Notably, meJA and ethylene (ET) treatments differentially expressed 93 and 60 HbCYP genes, respectively. Gene Ontology (GO) analysis and real-time quantitative polymerase chain reaction (RT-qPCR) validation of these genes revealed their significant contribution in rubber biosynthetic pathways. Protein interaction networks highlighted collaborations between HbCYPs and key rubber biosynthesis enzymes, including 3-hydroxy-3-methylglutaryl-CoA synthase (HMGS), and these results demonstrate functional diversification within the HbCYP family associated with rubber biosynthesis. Collectively, this study provides the first comprehensive genome-wide analysis of the HbCYP family in H. brasiliensis, offering insights into their evolutionary dynamics and functional diversification. The results establish a foundation for future research on CYP-mediated rubber biosynthesis and stress adaptation, with implications for molecular breeding of high-yield and stress-tolerant rubber tree cultivars.

Main conclusionNineTkOSCgenes have been identified by genome-wide screening. Among them,TkOSC4-6might be more crucial for natural rubber biosynthesis inTaraxacum kok-saghyzroots.Taraxacum kok-saghyz Rodin (TKS) roots contain large amounts of natural rubber, inulin, and valuable metabolites. Oxidosqualene cyclase (OSC) is a key member for regulating natural rubber biosynthesis (NRB) via the triterpenoid biosynthesis pathway. To explore the functions of OSC on natural rubber producing in TKS, its gene family members were identified in TKS genome via genome-wide screening. Nine TkOSCs were identified, which were mainly distributed in the cytoplasm. Their family genes experienced a neutral selection during the evolution process. Overall sequence homology analysis OSC proteins revealed 80.23% similarity, indicating a highly degree of conservation. Pairwise comparisons showed a multiple sequence similarity ranging from 57% to 100%. Protein interaction prediction revealed that TkOSCs may interact with baruol synthase, sterol 1,4-demethylase, lupeol synthase and squalene epoxidase. Phylogenetic analysis showed that OSC family proteins belong to two branches. TkOSC promoter regions contain cis-acting elements related to plant growth, stress response, hormones response and light response. Protein accumulation analysis demonstrated that TkOSC4, TkOSC5 and TkOSC6 proteins had strong expression levels in the root, latex and plumular axis. Comparison of gene expression patterns showed TkOSC1, TkOSC4, TkOSC5, TkOSC6, TkOSC7, TkOSC8 and TkOSC9 might be important in regulating NRB. Combination of gene and protein results revealed TkOSC4-6 might be more crucial, and the data might contribute to a more profound understanding of the roles of OSCs for NRB in TKS roots.

Natural rubber is an important industrial material, which is obtained from the only commercially cultivated rubber tree, Hevea brasiliensis. In rubber latex production, ethylene has been extensively used as a stimulant. Recent research showed that post-translational modifications (PTMs) of latex proteins, such as phosphorylation, glycosylation and ubiquitination, are crucial in natural rubber biosynthesis. In this study, comparative proteomics was performed to identify the glycosylated proteins in rubber latex treated with ethylene for different days. Combined with Pro-Q Glycoprotein gel staining and mass spectrometry techniques, we provided the first visual profiling of glycoproteomics of rubber latex and finally identified 144 glycosylated protein species, including 65 differentially accumulated proteins (DAPs) after treating with ethylene for three and/or five days. Gene Ontology (GO) functional annotation showed that these ethylene-responsive glycoproteins are mainly involved in cell parts, membrane components and metabolism. Pathway analysis demonstrated that these glycosylated rubber latex proteins are mainly involved in carbohydrate metabolism, energy metabolism, degradation function and cellular processes in rubber latex metabolism. Protein–protein interaction analysis revealed that these DAPs are mainly centered on acetyl-CoA acetyltransferase and hydroxymethylglutaryl-CoA synthase (HMGS) in the mevalonate pathway for natural rubber biosynthesis. In our glycoproteomics, three protein isoforms of HMGS2 were identified from rubber latex, and only one HMGS2 isoform was sharply increased in rubber latex by ethylene treatment for five days. Furthermore, the HbHMGS2 gene was over-expressed in a model rubber-producing grass Taraxacum Kok-saghyz and rubber content in the roots of transgenic rubber grass was significantly increased over that in the wild type plant, indicating HMGS2 is the key component for natural rubber production.