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Natural rubber (cis-1,4-polyisoprene) is a product of the isoprenoid biosynthesis pathway which requires an allylic pyrophosphate and isopentenyl pyrophosphate (IPP) to initiate and elongate the rubber molecule. The biosynthesis of IPP occurs via two distinct routes: the mevalonate (MVA) and methylerythritol phosphate (MEP) pathways. In this study, the expression of 34 genes related to rubber biosynthesis were compared between high and low latex yielding trees of two rubber tree clones, PB 217 and PB 260. Almost all tested genes revealed no significantly differential expression related to latex yield. Only mitochondrial pyruvate dehydrogenase (PDCE1) showed specific up-regulation in the high latex yielding trees of both tested clones. Interestingly, the expression of PDCE1 involving in the production of acetyl-CoA in mitochondria was also significantly induced by latex loss upon tapping. The increasing of acetyl-CoA and energy production may favor rubber tree to produce more latex. The in silico analysis showed that HbPDCE1 promoter contained ethylene and copper-responsive elements. Ethylene is worldwide used rubber stimulant while copper sulfate was also reported to be able to stimulate the latex yield. This suggested that HbPDCE1 may be transcriptionally regulated by these two compounds however the in vivo regulation of this gene should be further investigated. [ABSTRACT FROM AUTHOR]

The tapping panel dryness (TPD) syndrome of rubber is characterized by the reduction or ultimately total cessation of latex flow upon tapping, due to physiological disorders in the bark tissue. The protein pattern in the cytoplasm from healthy and TPD tree latex cells was compared by electrophoresis. Two polypeptides (P15 and P22) of 15 and 22 kDa, respectively, were found to accumulate in the cytosol of the TPD-affected trees, whereas a 29 kDa polypeptide (P29) appeared de novo. P15 and P22 were identified as REF (Hev b1) and SRPP (Hev b3), respectively, two proteins proposed to be involved in rubber biosynthesis. P29 appeared to be a new member of the patatin-like protein family. Specific molecular probes were designed for a detailed characterization of REF and SRPP gene expression and RFLP mapping. This allowed the demonstration that REF and SRPP display very similar expression profiles. They are highly over-expressed by the tapping-induced metabolic activation, although not by wounding per se, or ethylene or ABA. In addition to this similarity in gene expression, they were found to share one common locus in the genome. No significant difference in REF and SRPP gene expression was observed between healthy and TPD trees, indicating that their TPD-related accumulation in the cytosol was not transcriptionally regulated. Western blot analysis demonstrated that osmotic lysis of the sedimentable organelles (lutoids) in vitro caused the release of REF and SRPP from the rubber particle membrane into the cytosol. A mechanism of cellular delocalization as a consequence of the lutoids instability is proposed to explain REF and SRPP accumulation in the cytosol of TPD trees. [ABSTRACT FROM PUBLISHER]

Abstract: Natural rubber is synthesized in laticifers in the inner liber of the rubber tree (Hevea brasiliensis). Upon bark tapping, the latex is expelled due to liber turgor pressure. The mature laticifers are devoid of plasmodesmata; therefore a corresponding decrease in the total latex solid content is likely to occur due to water influx inside the laticifers. Auxins and ethylene used as efficient yield stimulants in mature untapped rubber trees, but, bark treatments with abscisic acid (ABA) and salicylic acid (SA) could also induce a transient increase latex yield. We recently reported that there are three aquaporin genes, HbPIP2;1, HbTIP1;1 and HbPIP1;1, that are regulated differentially after ethylene bark treatment. HbPIP2;1 was up-regulated in both the laticifers and the inner liber tissues, whereas HbTIP1;1 was up-regulated in the latex cells, but very markedly down-regulated in the inner liber tissues. Conversely, HbPIP1;1 was down-regulated in both tissues. In the present study, HbPIP2;1 and HbTIP1;1 showed a similar expression in response to auxin, ABA and SA, as seen in ethylene stimulation, while HbPIP1;1 was slightly regulated by auxin, but neither by ABA nor SA. The analysis of the HbPIP1;1 promoter region indicated the presence of only ethylene and auxin responsive elements. In addition, the poor efficiency of this HbPIP1;1 in increasing plasmalemma water conductance was confirmed in Xenopus oocytes. Thus, an increase in latex yield in response to all of these hormones was proposed to be the major function of aquaporins, HbPIP2;1 and HbTIP1;1. This study emphasized that the circulation of water between the laticifers and their surrounding tissues that result in latex dilution, as well as the probable maintenance of the liber tissues turgor pressure, favor the prolongation of latex flow. [ABSTRACT FROM AUTHOR]

Abstract: The cloning of hevein genes from Hevea brasiliensis was undertaken with the objective to isolate useful promoters to drive transgene expression in genetically engineered rubber tree. Four different full length genes were cloned by library screening and a fifth, a partial gene, by adaptor-anchored PCR. Sequence alignment revealed that hevein genes, although highly conserved in their transcribed region, diverged in two groups, with major differences in their promoter region, suggesting a more rapid evolution of the upstream regulatory functions of the genes than the downstream functions of their protein products. The promoter regions from two hevein genes representative of each group were isolated and analyzed in rice. Although both were functional, only the longest promoter sequence (PHev2.1) conferred a high level of expression to the transgene in various tissues of this heterologous host. It was in addition up-regulated by mechanical wounding and fungal infection in leaves. A number of potential cis-regulatory elements were identified in silico and are discussed in view of the expression profiles observed in rice. [Copyright &y& Elsevier]