Abstract
Hevea brasiliensis Muell. Arg, a member of the family Euphorbiaceae, is the sole natural resource exploited for commercial production of high-quality natural rubber. The properties of natural rubber latex are almost irreplaceable by synthetic counterparts for many industrial applications. A paucity of knowledge on the molecular mechanisms of rubber biosynthesis in high yield traits still persists. Here we report the comprehensive genome-wide analysis of the widely planted H. brasiliensis clone, RRIM 600. The genome was assembled based on ~155-fold combined coverage with Illumina and PacBio sequence data and has a total length of 1.55 Gb with 72.5% comprising repetitive DNA sequences. A total of 84,440 high-confidence protein-coding genes were predicted. Comparative genomic analysis revealed strong synteny between H. brasiliensis and other Euphorbiaceae genomes. Our data suggest that H. brasiliensis’s capacity to produce high levels of latex can be attributed to the expansion of rubber biosynthesis-related genes in its genome and the high expression of these genes in latex. Using cap analysis gene expression data, we illustrate the tissue-specific transcription profiles of rubber biosynthesis-related genes, revealing alternative means of transcriptional regulation. Our study adds to the understanding of H. brasiliensis biology and provides valuable genomic resources for future agronomic-related improvement of the rubber tree.
Highlights
The H. brasiliensis genome was characterized as high in repeat content and heterozygosity, and with a large genome size that poses technical challenges in assembling its genome
When compared with other Euphorbiaceae genomes, our analysis revealed that H. brasiliensis has the highest number of disease resistance-related genes
Our genomic and cap analysis gene expression (CAGE)-seq analyses offer some insights into the biological features that are unique to H. brasiliensis, those that are involved in rubber biosynthesis
Summary
The Pará rubber tree, or most commonly known as the rubber tree, is a medium to large monoecious and cross-pollinated tropical tree belonging to the family Euphorbiaceae (spurge)[1]. This family of flowering plants encompasses more than 7,500 species spread across 300 genera of herbs, shrubs and trees. Only H. brasiliensis yields an economically viable amount of latex that makes up most (99%) of the world’s natural rubber production. RRIM 600 is categorized as a medium yielding clone that produces ~1,350 kg of latex per hectare per year in estates over 20 years old. This clone shows moderate tolerance to cold, drought and wind, but is susceptible to disease caused by the pathogenic fungal Phytophthora spp. (http://www.rubberboard.org.in)
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