HbCOI1 perceives jasmonate to trigger signal transduction in Hevea brasiliensis

Natural rubber, a strategically essential raw material used in manufacturing throughout the world, is produced from coagulated and refined latex of rubber tree (Hevea brasiliensis). It is known that phytohormone jasmonate (JA) plays an essential role in regulating latex biosynthesis. However, it is unclear how the JA signal is sensed in a rubber tree. Here, we showed that Hevea brasiliensis CORONATINE-INSENSITIVE 1 (HbCOI1) acts as a receptor that perceives JA to recruit HbJAZ1 for signal transduction. We found that HbCOI1 restores male sterility and JA responses of the coi1–1 mutant in Arabidopsis. The identification of a JA receptor in the rubber tree is essential for elucidating the molecular mechanisms underlying JA-regulated latex biosynthesis. Our results elucidate the mechanism of JA perception in Hevea brasiliensis and also provide an efficient strategy to identify JA receptors in woody plants.

In situ 13CO2 labelling of rubber trees reveals a seasonal shift in the contribution of the carbon sources involved in latex regeneration

Rubber trees (Hevea brasiliensis) are the main source of natural rubber, extracted from latex, which exudes from the trunk after tapping. Tapped trees require large amounts of carbon (C) to regenerate the latex after its collection. Knowing the contribution of C sources involved in latex biosynthesis will help in understanding how rubber trees face this additional C demand. Whole crown 13CO2 pulse labelling was performed on 4-year-old rubber trees in June, when latex production was low, and in October, when it was high. 13C content was quantified in the foliage, phloem sap, wood, and latex. In both labelling periods, 13C was recovered in latex just after labelling, indicating that part of the carbohydrate was directly allocated to latex. However, significant amounts of 13C were still recovered in latex after 100 d and the peak was reached significantly later than in phloem sap, demonstrating the contribution of a reserve pool as a source of latex C. The contribution of new photosynthates to latex regeneration was faster and higher when latex metabolism was well established, in October, than in June. An improved understanding of C dynamics and the source–sink relationship in rubber tree is crucial to adapt tapping system practices and ensure sustainable latex production.

Proteomics analysis of latex from Hevea brasiliensis (clone RRIM 600)

The natural rubber latex extracted from the bark of Hevea brasiliensis plays various important roles in today’s modern society. Following ultracentrifugation, the latex can be separated into 3 layers: C-serum, lutoids, and rubber particles. Previous studies have shown that a large number of proteins are present in these 3 layers. However, a complete proteome for this important plant is still unavailable. Protein sequences have been recently translated from the completed draft genome database of H. brasiliensis, leading to the creation of annotated protein databases of the following H. brasiliensis biosynthetic pathways: photosynthesis, latex allergens, rubberwood formation, latex biosynthesis, and disease resistance. This research was conducted to identify the proteins contained within the latex by way of de novo sequencing from mass spectral data obtained from the 3 layers of the latex. Peptides from these proteins were fragmented using collision-induced dissociation, higher-energy collisional dissociation, and electron-transfer dissociation activation methods. A large percentage of proteins from the biosynthetic pathways (63% to 100%) were successfully identified. In addition, a total of 1839 unique proteins were identified from the whole translated draft genome database (AnnHBM).

Characterization of Hevea Brasiliensis Rubber from Virgin Trees: A Possible Role of Cis-Polyisoprene in Unexploited Tree

The role of rubber in Hevea brasiliensis was analyzed based on the structural analysis of rubber in rubber trees as latex. The rubber obtained from a mature-tree which has never tapped before, so-called “virgin mature-tree” (Vir-NR), contained the gel fraction higher than 80%, while that from a regularly tapped mature-tree (Reg-NR) was less than 3%. The gel showed almost the same structure as a crosslinked rubber prepared from fresh latex in the presence of peroxide, with the molecular weight between crosslinks (Mc) of 3×103. This value is extremely low comparing with that of 7×105 observed for the soft-gel in rubber from high-ammonia latex and Pale crepe. The sol fraction from Vir-NR was an oxidative degraded product containing aldehyde and epoxide groups. Aging properties of Vir-NR are much worse than those of Reg-NR. This indicates that rubber accepts free-radicals to form C-C crosslinking and partly oxidative scission of main-chains during storage in laticiferous tubes of Hevea trees. This suggests that a possible role of rubber is a scavenger of free-radicals in latex, due to lack of the naturally occurring antioxidants. The consecutive tappings of latex from the first opening mature-tree resulted in the formation of rubber similar to that obtained from Reg-NR, after six days. This modification indicates that the new regulation mechanisms in latex biosynthesis, which is induced by exploitation, can avoid the rubber chain crosslinkings and increase their elongations.