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Summary Natural rubber (NR) is a nonfungible and valuable biopolymer, used to manufacture ~50 000 rubber products, including tires and medical gloves. Current production of NR is derived entirely from the para rubber tree (Hevea brasiliensis). The increasing demand for NR, coupled with limitations and vulnerability of H. brasiliensis production systems, has induced increasing interest among scientists and companies in potential alternative NR crops. Genetic/metabolic pathway engineering approaches, to generate NR‐enriched genotypes of alternative NR plants, are of great importance. However, although our knowledge of rubber biochemistry has significantly advanced, our current understanding of NR biosynthesis, the biosynthetic machinery and the molecular mechanisms involved remains incomplete. Two spatially separated metabolic pathways provide precursors for NR biosynthesis in plants and their genes and enzymes/complexes are quite well understood. In contrast, understanding of the proteins and genes involved in the final step(s)—the synthesis of the high molecular weight rubber polymer itself—is only now beginning to emerge. In this review, we provide a critical evaluation of recent research developments in NR biosynthesis, in vitro reconstitution, and the genetic and metabolic pathway engineering advances intended to improve NR content in plants, including H. brasiliensis, two other prospective alternative rubber crops, namely the rubber dandelion and guayule, and model species, such as lettuce. We describe a new model of the rubber transferase complex, which integrates these developments. In addition, we highlight the current challenges in NR biosynthesis research and future perspectives on metabolic pathway engineering of NR to speed alternative rubber crop commercial development.

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.

Summary Rubber particles (RPs) are specialized organelles for the biosynthesis and storage of natural rubber in rubber‐producing plants. However, the mechanisms underlying the biogenesis and development of RPs remain unclear. In this study, two latex‐specific cis‐prenyltransferases (CPTs), TkCPT1 and TkCPT2, were identified in Taraxacum kok‐saghyz, with almost identical orthologues retained across other Taraxacum species. For the first time, Tkcpt1 single and Tkcpt1/2 double mutants were successfully generated using the CRISPR/Cas9 system. Rubber biosynthesis was significantly depressed in Tkcpt1 mutants and completely blocked in Tkcpt1/2 mutants. The absence of RPs in the Tkcpt1/2 was confirmed using oil red O and Nile red staining, high‐speed centrifugal stratification, cryo‐SEM and TEM on fresh latex or laticifer cells. Transcriptomic and proteomic analyses revealed that, in the latex of Tkcpt1/2, rubber biosynthesis was blocked at the protein level, while metabolomic profiling indicated an enrichment of lipids and terpenoids. Furthermore, knockout of TkCPTL1, a latex‐specific CPT‐like gene that encodes a rubber transferase activator, resulted in outright disruption of rubber biosynthesis and RP ontogeny, a phenotype similar to that of Tkcpt1/2 mutants. These findings indicate that rubber biosynthesis is a driving force for the biogenesis and development of RPs, providing new insights into rubber production mechanisms.

Rubber tree ( Hevea brasiliensis ) is the primary source of natural rubber and economically important. We present the haplotype-resolved, telomere-to-telomere, gap-free genome assembly of the cultivar CATAS 7-33–97, with both haplotypes containing complete telomeric and centromeric regions. Structural variations, including a 32.71 Mb inversion on chromosome 8, are identified. The fully assembled 36 chromosomes enable comprehensive identification of rubber biosynthesis genes and their allele-specific expression. By integrating transcriptomic and metabolomic data, we reconstruct the rubber biosynthesis pathway and confirm the mevalonate (MVA) pathway as the major carbon source for rapid latex regeneration during tapping. Jasmonic acid (JA) plays a key role in promoting rubber yield by enhancing biosynthetic activity in response to mechanical wounding. We propose a model where JA-induced myelocytomatosis proteins 2 activate mevalonate kinase 1 expression, boosting MVA synthesis and rubber production. These findings provide insights into rubber tree genomics and its molecular response to tapping. Authors report the assembly of the haplotype-resolved and telomere-to-telomere genome of a key rubber tree variety and uncover major structural variations. It is also revealed that jasmonic acid enhances rubber yield by activating the mevalonate pathway during tapping.

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.

Rubber residues present harmful impacts on health and environment, besides wasting valuable and huge amounts of rubber. Biological recycling technique is focused here to minimize this problem. A comparison of the biodegradation effect caused by Bacillus subtilis, Pseudomonas aeruginosa, and Streptomyces sp., separately, on vulcanized SBR-rubber during 4 weeks is reported. The surface and molecular analyses were studied by FTIR-ATR, TGA, DSC, TC and SEM/EDS, in addition to the contact angle and crosslinking tests. B. subtilis, P. aeruginosa, and Streptomyces sp. evoked after 4 weeks a loss in v-SBR crosslinks by 17.15, 10.68 and 43.39% and also in the contact angle with water by 14.10, 12.86 and 15.71%, respectively., if compared to Control samples. FTIR findings indicate that the polymeric chain has been partially consumed causing C-C bonds scission indicating the biodegradation and bio-devulcanization phenomena. The bacterial strains caused a carbon loss by 9.15, 5.97 and 4.55% after one week and 16.09, 16.79 and 18.13% after four weeks for B. subtilis, P. aeruginosa, and Streptomyces sp. mediums, respectively. DSC and EDS results are also promising and highlighting Streptomyces sp. strain as the most effective biodegradative one as an alternative and natural mean of degrading vulcanized rubber residues.

Bacterial degradation of natural rubber (NR) in an oxic environment is initiated by oxidative cleavage of double bonds in the NR-carbon backbone and is catalyzed by extracellular haem-containing rubber oxygenases. NR-cleavage products of sufficiently low molecular mass are taken up by the cells and metabolized for energy and biomass formation. Gram-negative and Gram-positive NR-degrading bacteria (usually) employ different types of rubber oxygenases such as RoxA and/or RoxB (most Gram-negative NR-degraders) or latex clearing protein Lcp (most Gram-positive NR-degraders). In order to find novel orthologues of Rox proteins, we have revisited databases and provide an update of Rox-like proteins. We describe the putative evolution of rubber oxygenases and confirm the presence of a third subgroup of Rox-related proteins (RoxCs), the biological function of which remains, however, unclear. We summarize the knowledge on the taxonomic position of Steroidobacter cummioxidans 35Y and related species. Comparison of genomic and biochemical features of strain 35Y with other species of the genus Steroidobacter suggests that strain 35Y represents a species of a novel genus for which the designation Aurantibaculum gen. nov. is proposed. A short summary on the capabilities of NR-degrading consortia, that could be superior in biotechnological applications compared to pure cultures, is also provided. Key points • Three types of rubber oxygenases exist predominantly in Gram-negative microbes • S. cummioxidans 35Y contains RoxA and RoxB which are superior in activity • S. cummioxidans 35Y represents a species of a novel genus

Main conclusion This study showed that MYC2 transcriptionally regulates valuable metabolites in Taraxacum spp . through direct interaction with specific target gene promoters. The Russian dandelion ( Taraxacum kok-saghyz ) represents a promising alternative species, capable of producing several high-added-value compounds, including natural rubber. Nevertheless, further enhancements are required for its optimal utilization by the industry. Here, we explored the role of the bHLH transcription factor TksMYC2, homolog of AtMYC2, in the regulation of the biosynthesis of specialized metabolites and free fatty acids and in the control of natural rubber production. Metabolic analyses of Taraxacum kok-saghyz plants showed that the overexpression of TksMYC2 significantly affected the accumulation of metabolites in roots and leaves, such as sesquiterpene lactones, phenylpropanoids, and free fatty acids. Moreover, overexpressing plants presented a significant increase in natural rubber production in both Taraxacum kok-saghyz and its related species Taraxacum brevicorniculatum . The direct interaction of TksMYC2 with the regulatory regions of cis-prenyltransferase 2 ( CPT2 ), small rubber particle proteins ( SRPP1 , SRPP3, and SRPP4 ), involved in the biosynthesis of natural rubber, and with the germacrene A oxidase ( GAO ), involved in the biosynthesis of sesquiterpenes, was demonstrated by chromatin immunoprecipitation coupled with quantitative PCR. Additionally, these genes were highly induced in the lines overexpressing TksMYC2 . Our findings suggest that TksMYC2 and its downstream components may be valid targets for breeding programmes to increase the production of valuable metabolites, including natural rubber.

The para rubber tree ( Hevea brasiliensis ) is the world’s sole commercial source of natural rubber, a vital industrial raw material. However, the narrow genetic diversity of this crop poses challenges for rubber breeding. Here, we generate high-quality de novo genome assemblies for three H. brasiliensis cultivars, two H. brasiliensis wild accessions, and three other Hevea species ( H. nitida , H. pauciflora , and H. benthamiana ). Through analyzing genomes of 94 Hevea accessions, we identify five distinct lineages that do not align with their previous species delineations. We discover multiple accessions with hybrid origins between these lineages, indicating incomplete reproductive isolation between them. Only two out of four wild lineages have been introduced to commercial rubber cultivars. Furthermore, we reveal that the rubber production traits emerged following the development of a large REF/SRPP gene cluster and its functional specialization in rubber-producing laticifers within this genus. These findings would enhance rubber breeding and benefit research communities. The para rubber tree is the world’s sole commercial source of natural rubber. Here, the authors assemble the pangenome based on five genomes of H. brasiliensis and three genomes of other Hevea species, and reveal species delineation and rubber trait evolution through phylogenomic analyses.

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.