Abstract
The Para rubber tree (Hevea brasiliensis) is an economically important tropical tree species that produces natural rubber, an essential industrial raw material. Here we present a high-quality genome assembly of this species (1.37 Gb, scaffold N50 = 1.28 Mb) that covers 93.8% of the genome (1.47 Gb) and harbours 43,792 predicted protein-coding genes. A striking expansion of the REF/SRPP (rubber elongation factor/small rubber particle protein) gene family and its divergence into several laticifer-specific isoforms seem crucial for rubber biosynthesis. The REF/SRPP family has isoforms with sizes similar to or larger than SRPP1 (204 amino acids) in 17 other plants examined, but no isoforms with similar sizes to REF1 (138 amino acids), the predominant molecular variant. A pivotal point in Hevea evolution was the emergence of REF1, which is located on the surface of large rubber particles that account for 93% of rubber in the latex (despite constituting only 6% of total rubber particles, large and small). The stringent control of ethylene synthesis under active ethylene signalling and response in laticifers resolves a longstanding mystery of ethylene stimulation in rubber production. Our study, which includes the re-sequencing of five other Hevea cultivars and extensive RNA-seq data, provides a valuable resource for functional genomics and tools for breeding elite Hevea cultivars.
Highlights
The Para rubber tree (Hevea brasiliensis) is an economically important tropical tree species that produces natural rubber, an essential industrial raw material
When considering other rubber-producing plants, eight REF/SRPP genes are identified in Lactuca sativa and six in limited expressed sequence tag (EST)/mRNA sequences of Parthenium argentatum (Supplementary Table 19). These results suggest a possible link between expansion of the REF/SRPP family and the ability to produce rubber
Clade 1 isoforms were clustered into an independent clade whereas the remainder were scattered together with the homologues from other plants into different clades (Supplementary Fig. 17). These results suggest that the clade 1 REF/SRPP genes might have evolved independently towards functioning in rubber biosynthesis
Summary
The Para rubber tree (Hevea brasiliensis) is an economically important tropical tree species that produces natural rubber, an essential industrial raw material. We report a high-quality genome assembly of Hevea Reyan[7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33-97], an elite cultivar widely planted in China[12,13] based on sequence data from both whole-genome shotgun (WGS) and pooled BAC clones This assembly contains 7,453 scaffolds (N50 = 1.28 Mb), has a length of 1.37 Gb and covers ∼94% of the predicted genome size (1.46 Gb). Together with analysis of data from re-sequencing five other cultivars and comprehensive transcriptomic surveys, we aim to obtain new insights into the physiology of laticifers and molecular details of rubber biosynthesis, especially in relation to ethylene-stimulated rubber production
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