橡胶草90年来主要研究成果及最新研究进展

天然橡胶是重要的国防战略物质,巴西橡胶树（Hevea brasiliensis（Willd.ex A.Juss.） Muell.Arg）是天然橡胶的唯一来源,天然橡胶商业化形式极为单一,潜在的供给不足问题亟待解决。因此,寻找可替代巴西橡胶树的产胶植物一直受到全世界高度重视。蒲公英属橡胶草（Taraxacum kok-saghyz Rodin）根部含有与橡胶树橡胶类似的天然橡胶分子,该植物主要分布在温带和寒带地区,具有易于机械化收获、生长周期短、遗传转化相对容易等特点,是最具开发潜力的产胶植物。本文对橡胶草90年（1931-2018）来的研究历史和主要成果进行了概括,对近10年取得的最新成果进行了深度分析,并预测橡胶草在未来天然橡胶产业中的作用,期望为开展橡胶草商业化生产和橡胶生物合成相关基础研究提供一定的参考。     

橡胶草90年来主要研究成果及最新研究进展

天然橡胶是重要的国防战略物质,巴西橡胶树( Hevea brasiliensis (Willd. ex A. Juss.) Muell. Arg)是天然橡胶的唯一来源,天然橡胶商业化形式极为单一,潜在的供给不足问题亟待解决。因此,寻找可替代巴西橡胶树的产胶植物一直受到全世界高度重视。蒲公英属橡胶草( Taraxacum kok-saghyz Rodin)根部含有与橡胶树橡胶类似的天然橡胶分子,该植物主要分布在温带和寒带地区,具有易于机械化收获、生长周期短、遗传转化相对容易等特点,是最具开发潜力的产胶植物。本文对橡胶草90年(1931 - 2018)来的研究历史和主要成果进行了概括,对近10年取得的最新成果进行了深度分析,并预测橡胶草在未来天然橡胶产业中的作用,期望为开展橡胶草商业化生产和橡胶生物合成相关基础研究提供一定的参考。     

Guayule and Russian dandelion as alternative sources of natural rubber

Natural rubber, obtained almost exclusively from the Para rubber tree (Hevea brasiliensis), is a unique biopolymer of strategic importance that, in many of its most significant applications, cannot be replaced by synthetic rubber alternatives. Several pressing motives lead to the search for alternative sources of natural rubber. These include increased evidence of allergenic reactions to Hevea rubber, the danger that the fungal pathogen Microcyclus ulei, causative agent of South American Leaf Blight (SALB), might spread to Southeast Asia, which would severely disrupt rubber production, potential shortages of supply due to increasing demand and changes in land use, and a general trend towards the replacement of petroleum-derived chemicals with renewables. Two plant species have received considerable attention as potential alternative sources of natural rubber: the Mexican shrub Guayule (Parthenium argentatum Gray) and the Russian dandelion (Taraxacum koksaghyz). This review will summarize the current production methods and applications of natural rubber (dry rubber and latex), the threats to the production of natural rubber from the rubber tree, and describe the current knowledge of the production of natural rubber from guayule and Russian dandelion.     

Guayule and Russian Dandelion as Alternative Sources of Natural Rubber

ABSTRACT

Natural rubber, obtained almost exclusively from the Para rubber tree (Hevea brasiliensis), is a unique biopolymer of strategic importance that, in many of its most significant applications, cannot be replaced by synthetic rubber alternatives. Several pressing motives lead to the search for alternative sources of natural rubber. These include increased evidence of allergenic reactions to Hevea rubber, the danger that the fungal pathogen Microcyclus ulei, causative agent of South American Leaf Blight (SALB), might spread to Southeast Asia, which would severely disrupt rubber production, potential shortages of supply due to increasing demand and changes in land use, and a general trend towards the replacement of petroleum-derived chemicals with renewables. Two plant species have received considerable attention as potential alternative sources of natural rubber: the Mexican shrub Guayule (Parthenium argentatum Gray) and the Russian dandelion (Taraxacum koksaghyz). This review will summarize the current production methods and applications of natural rubber (dry rubber and latex), the threats to the production of natural rubber from the rubber tree, and describe the current knowledge of the production of natural rubber from guayule and Russian dandelion.     

Initiator-independent and initiator-dependent rubber biosynthesis in Ficus elastica

The rubber-producing tree, Ficus elastica (the Indian rubber tree), requires the same substrates for rubber production as other rubber-producing plants, such as Hevea brasiliensis (the Brazilian or Para rubber tree), the major source of commercial natural rubber in the world, and Parthenium argentatum (guayule), a widely studied alternative for natural rubber production currently under commercial development. Rubber biosynthesis can be studied, in vitro, using purified, enzymatically active rubber particles, an initiator such as FPP, IPP as the source of monomer, and a metal cofactor such as Mg2+. However, unlike H. brasiliensis and P. argentatum, we show that enzymatically active rubber particles purified from F. elastica are able to synthesize rubber, in vitro, in the absence of added initiator. In this paper, we characterize, for the first time, the kinetic differences between initiator-dependent rubber biosynthesis, and initiator-independent rubber biosynthesis, and the effect of cofactor concentration on both of these processes.     

巴西橡胶树的分子生物学研究进展

巴西橡胶树是一种重要的热带经济作物,由于橡胶树体内橡胶含量多,且容易采收,所以橡胶树一直是天然橡胶的商业来源。相比于模式植物和粮食等经济作物来说,分子生物学研究显滞后。,而且橡胶树是多年生乔木,经济性状多集中于胶乳,因此研究难度大,研究也不多,本就巴西橡胶的分子生物学方面的研究进行综述。     

Alternative sources of natural rubber

Rubber (cis-1,4-polyisoprene) is one of the most important polymers naturally produced by plants because it is a strategic raw material used in more than 40,000 products, including more than 400 medical devices. The sole commercial source, at present, is natural rubber harvested from the Brazilian rubber tree, Hevea brasiliensis. Primarily due to its molecular structure and high molecular weight (>1 million daltons) this rubber has high performance properties that cannot easily be mimicked by artificially produced polymers, such as those derived from, e.g., bacterial poly-hydroxy-alkanoates (PHAs). These high performance properties include resilience, elasticity, abrasion resistance, efficient heat dispersion (minimizing heat build-up under friction), and impact resistance. Medical rubber gloves need to fit well, be break-resistant, allow the wearer to retain fine tactile sensation, and provide an effective barrier against pathogens. The sum of all these characteristics cannot yet be achieved using synthetic gloves. The lack of biodiversity in natural rubber production renders continuity of supply insecure, because of the risk of crop failure, diminishing acreage, and other disadvantages outlined below. A search for alternative sources of natural rubber production has already resulted in a large number of interesting plants and prospects for immediate industrial exploitation of guayule (Parthenium argentatum) as a source of high quality latex. Metabolic engineering will permit the production of new crops designed to accumulate new types of valued isoprenoid metabolites, such as rubber and carotenoids, and new combinations extractable from the same crop. Currently, experiments are underway to genetically improve guayule rubber production strains in both quantitative and qualitative respects. Since the choice for gene activities to be introduced or changed is under debate, we have set up a complementary approach to guayule with yeast species, which may more quickly show the applicability and relevance of genes selected. Although economic considerations may prevent commercial exploitation of new rubber-producing microorganisms, transgenic yeasts and bacteria may yield intermediate or alternative (poly-)isoprenes suitable for specific applications. Received: 9 August 1999 / Received revision: 15 October 1999 / Accepted: 16 October 1999     

Regulation of Natural Rubber Biosynthesis by Proteins Associated with Rubber Particles

Natural rubber, cis-1,4-polyisoprene, is an essential raw material used in thousands of products, many of which are absolutely necessary for medical purposes. Natural rubber is obtained from latex, an aqueous emulsion present in the laticiferous vessels of the natural rubber-producing plants. Hevea brasiliensis (the Brazilian rubber tree) currently is the only commercially important source of natural rubber. H. brasiliensis crops have very little genetic variability, leaving rubber plantations at risk of serious pathogenic attacks. In addition, repeated exposure to residual proteins in latex products derived from H. brasiliensis have led to serious and widespread allergic (type I) hypersensitivity. Therefore, identification of alternative sources of natural rubber is a very important biotechnological task. Potentially, Russian dandelion (Taraxacum kok-saghyz) may be such an alternative because significant amounts of natural rubber are produced in its root system. However, H. brasiliensis is a more efficient producer of natural rubber than T. kok-saghyz. Thus, improvement of rubber biosynthesis in plants is a first-priority problem of modern biotechnology. In this review, we describe proteins that may increase the concentration of natural rubber in laticiferous vessels of T. kok-saghyz and its close relative Taraxacum brevicorniculatum, when overexpressed in the plants. These proteins, cis-prenyltransferases, rubber transferase activator, and small rubber particle proteins, are directly involved in synthesis of the polyisoprene chain. We also analyze the effects of their expression levels on the production of natural rubber in vivo.     

Influence of cerrado fragments in the distribution of mites in rubber tree crop

The aim of this study was to verify whether fragments of cerrado influence the composition of the mite fauna on rubber trees. Five transects distant 50 m, being the first in the edge near the native areas and the last 200 m inside the crop, were established in each rubber tree crop in southern State of Mato Grosso. In each transect five plants were chosen, and seven leaves were collected from each plant. During one year, 25 quantitative samplings were conducted in two rubber tree crops. The lowest number of phytophagous mites occurred in the transect closer to the native vegetation, and the highest number, in the most distant from the native vegetation. The largest diversity was also observed in the transect closer to the neighboring vegetation. Ten species of predatory mites were also registered in neighboring native areas. These data suggest the movement of predatory mites from the native areas to the monoculture. These natural areas can possibly supply alternative food and habitat for natural enemies of phytophagous mites in the period of food scarceness in the rubber tree crop. The presence of native areas close to culture areas should be taken into account in the elaboration of programs of ecological management of pests.     

Natural rubber biosynthesis in plants,the rubber transferase complex,and metabolic engineering progress and prospects

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.     

橡胶草的研究进展

天然橡胶是一种不可替代的重要战略工业原料, 用途广泛。巴西橡胶树作为天然橡胶的主要来源, 受种植面积限制, 难以满足全球日益增长的对天然橡胶的需求。而南美叶疫病也是巴西橡胶树(Hevea brasiliensis)安全的潜在威胁。蒲公英属产胶植物(橡胶草)最早发现于20世纪30年代, 可产生高质量的天然橡胶, 具有生长周期短、地理适应范围广、适合机械化生产等特点, 被认为是一种理想的产胶备选作物。该文从橡胶草种质资源、遗传改良、栽培技术及产胶生物学机制等方面综述了国内外橡胶草的研究进展和存在的问题, 并为我国开展橡胶草相关研究提出建议。     

SNP Identification from RNA Sequencing and Linkage Map Construction of Rubber Tree for Anchoring the Draft Genome

Hevea brasiliensis, or rubber tree, is an important crop species that accounts for the majority of natural latex production. The rubber tree nuclear genome consists of 18 chromosomes and is roughly 2.15 Gb. The current rubber tree reference genome assembly consists of 1,150,326 scaffolds ranging from 200 to 531,465 bp and totalling 1.1 Gb. Only 143 scaffolds, totalling 7.6 Mb, have been placed into linkage groups. We have performed RNA-seq on 6 varieties of rubber tree to identify SNPs and InDels and used this information to perform target sequence enrichment and high throughput sequencing to genotype a set of SNPs in 149 rubber tree offspring from a cross between RRIM 600 and RRII 105 rubber tree varieties. We used this information to generate a linkage map allowing for the anchoring of 24,424 contigs from 3,009 scaffolds, totalling 115 Mb or 10.4% of the published sequence, into 18 linkage groups. Each linkage group contains between 319 and 1367 SNPs, or 60 to 194 non-redundant marker positions, and ranges from 156 to 336 cM in length. This linkage map includes 20,143 of the 69,300 predicted genes from rubber tree and will be useful for mapping studies and improving the reference genome assembly.     

气候变化背景下橡胶树物候研究进展

橡胶树(Heveabrasiliensis)是广布于热带地区的经济林木，是战略物资天然橡胶的主要来源，其物候学的研究对胶园生产管理和评估热带地区植被对全球气候变化的响应方面具有重要意义。早期的物候研究主要服务于苗木繁育、割胶规划和抗逆栽培等生产应用；利用遥感监测植被物候日趋成熟，已广泛应用于橡胶树并成为主流的物候监测方法；橡胶树物候具有明显的时空异质性，对气候变化的响应较为复杂，其中温度和降水是关键影响因子，同时内因(品系、基因和树龄等)和外因(种植密度、地理位置和农业措施等)也共同影响了其物候。为更好服务天然橡胶产业的可持续发展和热区气候变化科学研究，未来的橡胶树物候研究应重点关注多源遥感数据的协同重建、物候指标提取算法的普适化和遥感预测模型的精准化。该文系统梳理了橡胶树物候的监测方法、服务价值、时空格局，提出了存在问题及未来研究方向。     

Production of rubber-like polymers by microorganisms

Biopolymers with true rubber properties are exceptionally rare in prokaryotic microorganisms. Only some polyhydroxyalkanoic acids are thermoplastic elastomers within a narrow temperature range that can be extended by crosslinking. Other polyhydroxyalkanoic acids are rigid and need specific thermal treatment during annealing to yield elastomeric materials. The most important elastomer is natural rubber (cis-1,4-polyisoprene). The rubber tree Hevea brasiliensis is so far the only relevant commercial source of this polymer, although many other plants are also capable of its synthesis. Recent advances in the analysis of isoprenoid and polyisoprene biosynthesis pathways have encouraged attempts to establish production of natural rubber in bacteria. Establishment of functional cis-1,4-polyisoprene biosynthesis pathways in bacteria depends firstly on the biosynthesis of isoprene moieties via the mevalonate or methylerythritol phosphate pathway and secondly on the polymerisation of isoprene moieties by a prenyltransferase yielding high-molecular-weight polyisoprenoids. The genes that encode prenyltransferases are as yet unknown and so the establishment of such a pathway and formation of rubber in recombinant bacteria will be a difficult task.     

Identification of natural rubber and characterization of rubber biosynthetic activity in fig tree

Natural rubber was extracted from the fig tree (Ficus carica) cultivated in Korea as part of a survey of rubber producing plants. Fourier transform infrared and (13)C nuclear magnetic resonance analysis of samples prepared by successive extraction with acetone and benzene confirmed that the benzene-soluble residues are natural rubber, cis-1,4-polyisoprene. The rubber content in the latex of fig tree was about 4%, whereas the rubber content in the bark, leaf, and fruit was 0.3%, 0.1%, and 0.1%, respectively. Gel-permeation chromatography revealed that the molecular size of the natural rubber from fig tree is about 190 kD. Similar to rubber tree (Hevea brasiliensis) and guayule (Parthenium argentatum Gray), rubber biosynthesis in fig tree is tightly associated with rubber particles. The rubber transferase in rubber particles exhibited a higher affinity for farnesyl pyrophosphate than for isopentenyl pyrophosphate, with apparent K(m) values of 2.8 and 228 microM, respectively. Examination of latex serum from fig tree by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed major proteins of 25 and 48 kD in size, and several proteins with molecular mass below 20 and above 100 kD. Partial N-terminal amino acid sequencing and immunochemical analyses revealed that the 25- and 48-kD proteins were novel and not related to any other suggested rubber transferases. The effect of EDTA and Mg(2+) ion on in vitro rubber biosynthesis in fig tree and rubber tree suggested that divalent metal ion present in the latex serum is an important factor in determining the different rubber biosynthetic activities in fig tree and rubber tree.     

Identification and characterization of genes associated with tapping panel dryness from <Emphasis Type="Italic">Hevea brasiliensis</Emphasis>latex using suppression subtractive hybridization

Background  

Tapping panel dryness (TPD) is one of the most serious threats to natural rubber production. Although a great deal of effort has been made to study TPD in rubber tree, the molecular mechanisms underlying TPD remain poorly understood. Identification and systematical analyses of the genes associated with TPD are the prerequisites for elucidating the molecular mechanisms involved in TPD. The present study is undertaken to generate information about the genes related to TPD in rubber tree.     

Alternate industrial feedstocks from agriculture

Before the rapid development of the petrochemical industry, many feedstocks for manufacturing paints, plastics, fibers, lubricants, adhesives, and a host of other products were derived from agriculture. Good examples are linseed, castor, tung, tall, and soybean oils; natural rubber, gums, starch and cellulose, and many sources of fiber from the plant kingdom, as well as hides, bones, and fats and oils from the animal kingdom. In addition to these traditional agricultural materials, several new plant sources have been developed through new crops research. Also, new ways have been developed for converting existing agricultural products to better chemical intermediates. Availability of farm land, economics of crop production, and competition with petroleum are such that agriculture should be considered seriously as a viable alternative for at least part of our chemical feedstock requirements.     

Quantifying above‐ and belowground biomass carbon loss with forest conversion in tropical lowlands of Sumatra (Indonesia)

Natural forests in South‐East Asia have been extensively converted into other land‐use systems in the past decades and still show high deforestation rates. Historically, lowland forests have been converted into rubber forests, but more recently, the dominant conversion is into oil palm plantations. While it is expected that the large‐scale conversion has strong effects on the carbon cycle, detailed studies quantifying carbon pools and total net primary production (NPP_total) in above‐ and belowground tree biomass in land‐use systems replacing rainforest (incl. oil palm plantations) are rare so far. We measured above‐ and belowground carbon pools in tree biomass together with NPP_total in natural old‐growth forests, ‘jungle rubber’ agroforests under natural tree cover, and rubber and oil palm monocultures in Sumatra. In total, 32 stands (eight plot replicates per land‐use system) were studied in two different regions. Total tree biomass in the natural forest (mean: 384 Mg ha^?1) was more than two times higher than in jungle rubber stands (147 Mg ha^?1) and >four times higher than in monoculture rubber and oil palm plantations (78 and 50 Mg ha^?1). NPP_total was higher in the natural forest (24 Mg ha^?1 yr^?1) than in the rubber systems (20 and 15 Mg ha^?1 yr^?1), but was highest in the oil palm system (33 Mg ha^?1 yr^?1) due to very high fruit production (15–20 Mg ha^?1 yr^?1). NPP_total was dominated in all systems by aboveground production, but belowground productivity was significantly higher in the natural forest and jungle rubber than in plantations. We conclude that conversion of natural lowland forest into different agricultural systems leads to a strong reduction not only in the biomass carbon pool (up to 166 Mg C ha^?1) but also in carbon sequestration as carbon residence time (i.e. biomass‐C:NPP‐C) was 3–10 times higher in the natural forest than in rubber and oil palm plantations.     

Characterization of polymorphic microsatellite markers for Microcyclus ulei,causal agent of South American leaf blight of rubber trees

South American leaf blight caused by the ascomycete Microcyclus ulei is the most harmful disease of the rubber tree in Latin America and a potential threat to Asiatic and African natural rubber production. Until now, the variability of this fungus was assessed through observation of pathogenicity of isolates on a range of rubber tree clones with known resistance reactions. The present study describes the process used to design 11 microsatellite markers and evaluates their usefulness in detecting genetic polymorphism. Nine of these markers were polymorphic among six isolates from Brazil (with two to three alleles per locus) and five markers were polymorphic among four isolates from French Guiana (with two to four alleles per locus).     

Ethylene stimulation of latex production in Hevea brasiliensis

Rubber tree (Hevea brasiliensis) is an important industrial crop for natural rubber production. Ethylene, as a stimulant of latex production in H. brasiliensis, has been widely used in commercial latex production. However, the mechanism of ethylene action are not completely elucidated, especially in molecular aspect. Here, we focus on the molecular biological progression of ethylene stimulation of latex production. Our data and all previous information showed ethylene had little direct effect on accelerating rubber biosynthesis. The prolonged latex flow and acceleration of sucrose metabolism by ethylene may be the main reasons for the stimulation of latex yield by ethylene.Key words: Hevea brasiliensis, ethylene, rubber production, gene, sucrose