Hevea brasiliensis
Overview
Hevea brasiliensis, a large evergreen arbor in the family Euphorbiaceae, is an important crop in tropical areas. Rubber has a variety of good special properties, such as elasticity, insulation, abrasion resistance, air tightness, flexibility and so on. Therefore, it is extensively used and well-known as "black gold". Rubber trees are mainly propagated by seeds, and their growth requires conditions of still winds, high temperatures and high humidity. Natural rubber is an agricultural product and in the long term its production is mainly influenced by the growth cycle and cutting efficiency; in the short term, weather conditions and policy changes can have an impact on production
Geographical Distribution
Rubber trees originated in the Amazon Basin of South America, and archaeological excavations indicate that people have been using natural rubber since the 11th century there. The earliest introduction of rubber trees in China dates back to 1904 and the sizable practical production began in 1952, almost seventy years ago.
At present, rubber trees are mainly distributed in Thailand, Malaysia, China, India, Indonesia, Vietnam, Nigeria, Brazil, Sri Lanka and other countries. The largest area for rubber trees cultivation is in Southeast Asia, with 62.9% of global production in Thailand and Indonesia. In China, rubber is cultivated widely in Hainan and southern Yunnan, as well as Taiwan, southern Fujian, Guangdong and Guangxi.
Application
- Industrial raw material: Most of the natural rubber used in the world is produced from rubber trees. Milky white sap called latex flows out when the bark of a rubber tree is cut, and after coagulation, washing, molding and drying it will turn into natural rubber. For this purpose, the Hevea brasiliensis trees are mostly cultivated. Natural rubber has a good quality of high elasticity and good insulation, plasticity, water and air insulation, tensile and abrasion resistance, thus being used in a wide range of applications in industry, national defence, transportation and other aspects in everyday life.
- Edible use: Rubber seed oil is a traditional edible oil in rubber growing areas around the world, and has a long history of consumption in Xishuangbanna, Yunnan Province and Hainan Province in China. It is rich in nutrients, which main components include soft fatty acid, stearic acid, oleic acid, linoleic acid, linolenic acid and so on. It has a fair proportion of various fatty acids, and it has been researched and proven to have a good effect in lowering the blood lipid.
- Construction: Rubber trees has a low density, with beautiful patterns and good processing properties. It can be chemically treated to make fine furniture, fibreboard, plywood, paper pulp and so on.
Genome sequencing
The H. brasiliensis clone RRIM 600, which was developed by the Rubber Research Institute of Malaysia, is a high-yielding clone. In 2013, the Centre for Chemical Biology at the University of Penang, Malaysia, generated a draft of its fragmented genome sequence. The researchers utilized the Whole Genome Shotgun (WGS) method and obtained sequence data from the Roche 454, Illumina, and SOLiD platforms. The assembly resulted in a scaffold of 1,119 Mb, with a scaffold N50 of 2,972 bp. Through the use of 154 microsatellite markers, 143 scaffolds and their associated 1,325 genes were successfully anchored to 18 rubber tree linkage groups. Additionally, a model containing 68,955 genes was predicted.
The Centre for Chemical Biology at Universiti Teknologi Malaysia made significant improvements to the assembly of the RRIM 600 genome in 2016. The new genome assembly was based on approximately 155-fold combinatorial coverage of Illumina and PacBio sequence data. The size of the genome is 1.55 Gb, with 72.5% comprising repetitive DNA sequences. The assembly consisted of 189,316 scaffolds, with an N50 size of 67.2 Kb. In comparison to previously published genome assemblies, the N50 size increased by 23-fold, and the number of scaffolds decreased by 3-fold. A total of 84,440 high-confidence protein-coding genes were predicted.
The rubber tree variety Reyan 7-33-97 is an elite cultivar widely grown in China. The Rubber Research Institute of the Chinese Academy of Tropical Agricultural Sciences led the assembly of the genetic draft in 2016. The genetic draft was generated through whole genome shotgun sequencing and pooled BAC clones. The assembly consists of 7,453 scaffolds, with a scaffold N50 of 1.28 Mb and a total length of 1.37 Gb, encompassing 43,792 protein-coding genes.
The rubber tree variety BPM24 has demonstrated remarkable resistance against two major fungal pathogens prevalent in Southeast Asia, namely Blastomyces and Corynebacterium. The National Genetic Engineering and Biotechnology Center of Thailand (BIOTEC) and the Rubber Authority of Thailand collaborated to successfully sequence the reference genome of this variety in 2017. The reference genome was generated using a combination of deep-coverage 454/Illumina short-reads and Pacific Biosciences (PacBio) long-reads sequencing technologies, resulting in a sequencing depth of approximately 68X. This comprehensive sequencing approach resulted in a preliminary draft of the genome. Subsequently, the "Chicago" technology was employed for long-range scaffolding, yielding a final assembly of 1.26 Gb with an N50 size of 96.8 kb. The assembled genome consists of 69.2% repetitive sequences and exhibits a GC content of 34.31%.
The rubber variety GT1 is an elite variety cultivated worldwide. In 2020, the Kunming Institute of Botany, Chinese Academy of Sciences, in collaboration with UW Genetics, successfully completed the reference genome for GT1. The sequencing technologies employed in this study included Illumina, PacBio, and Hi-C, enabling the generation of a high-quality reference genome for the rubber tree at the chromosome level. The resulting genome has a size of 1.47GB and exhibits a contig N50 of 152.7kb.
Reference
1.中国科学院中国植物志委员会. 中国植物志.第44卷[M]. 科学出版社, 1996.
2.百度百科：https://baike.baidu.com/item/%E6%A9%A1%E8%83%B6%E6%A0%91/742959?fr=aladdin
3.Rahman AY, Usharraj AO, Misra BB, et al. Draft genome sequence of the rubber tree Hevea brasiliensis. BMC Genomics. 2013;14:75. [OpenLBID: OLB-PM-23375136]
4.Lau NS, Makita Y, Kawashima M, et al. The rubber tree genome shows expansion of gene family associated with rubber biosynthesis. Sci Rep. 2016;6:28594. [OpenLBID: OLB-PM-27339202]
5.Tang C, Yang M, Fang Y, et al. The rubber tree genome reveals new insights into rubber production and species adaptation. Nat Plants. 2016;2(6):16073. [OpenLBID: OLB-PM-27255837]
6.Pootakham W, Sonthirod C, Naktang C, et al. De novo hybrid assembly of the rubber tree genome reveals evidence of paleotetraploidy in Hevea species. Sci Rep. 2017;7:41457. [OpenLBID: OLB-PM-28150702]
7.Liu J, Shi C, Shi CC, et al. The Chromosome-Based Rubber Tree Genome Provides New Insights into Spurge Genome Evolution and Rubber Biosynthesis. Mol Plant. 2020;13(2):336-350. [OpenLBID: OLB-PM-31838037]