Metabolic routes affecting rubber biosynthesis in Hevea brasiliensis latex

Abstract

The cytosolic mevalonate (MVA) pathway in Hevea brasiliensis latex is the conventionally accepted pathway which provides isopentenyl diphosphate (IPP) for cis-polyisoprene (rubber) biosynthesis. However, the plastidic 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway may be an alternative source of IPP since its more recent discovery in plants. Quantitative RT-PCR (qRT-PCR) expression profiles of genes from both pathways in latex showed that subcellular compartmentalization of IPP for cis-polyisoprene synthesis is related to the degree of plastidic carotenoid synthesis. From this, the occurrence of two schemes of IPP partitioning and utilization within one species is proposed whereby the supply of IPP for cis-polyisoprene from the MEP pathway is related to carotenoid production in latex. Subsequently, a set of latex unique gene transcripts was sequenced and assembled and they were then mapped to IPP-requiring pathways. Up to eight such pathways, including cis-polyisoprene biosynthesis, were identified. Our findings on pre- and post-IPP metabolic routes form an important aspect of a pathway knowledge-driven approach to enhancing cis-polyisoprene biosynthesis in transgenic rubber trees.

Draft genome sequence of the rubber tree Hevea brasiliensis

“…Recently, 13 C-labelled studies on Hevea seedlings suggested that the MEP pathway contributes IPP for carotenoid biosynthesis, but not for rubber biosynthesis [35]. However, expression analysis on MVA and MEP pathway genes suggest that the MEP pathway can be an alternate provider of IPP in mature rubber trees or in clones which do not produce a large amount of carotenoid [8]. In the H. brasiliensis genome, we identified 18 genes encoding enzymes for the MVA pathway and 29 for the MEP pathway.…”

Hevea brasiliensis REF (Hev b 1) and SRPP (Hev b 3): An overview on rubber particle proteins

“…More recently, Priya et al however showed that at least REF gene expression was inducible by both tapping and ethephon treatment, and that the latex yield was indeed correlated with REF expression [65]. Lately, the induction of both REF and SRPP expression after ethephon treatment was confirmed, which also correlates with increased NR synthesis [9].…”

“…For reviews on the enzymatic catalysis of NR biosynthesis and structure see Refs. [9,76,79,80]. Many proteins and enzymes are involved in this process, including IPP isomerase, cis-prenyl transferases and synthases also found in latex.…”

“…It should also be noted that Frey-Wyssling yellow particles (because of their carotenoid-rich content) have also been associated with the bottom fraction of certain hevea clones (e.g. PB 235) [8,9].…”

HbMADS4, a MADS-box Transcription Factor from Hevea brasiliensis, Negatively Regulates HbSRPP

“…NR (a cis 1, 4-polyisoprene) biosynthesis occurs on rubber particles suspended in rubber tree laticifers (d’Auzac et al, 1989). Latex (cytoplasmic content of laticifers) contants 30–50% cis -polyisoprene which is synthetized through the mevalonate pathway (Chow et al, 2007, 2012; Sando et al, 2008). The NR biosynthesis is a typical isoprenoid secondary metabolism which is similar to the isoprenoid biosynthesis of other plants (Chow et al, 2007).…”