Abstract
BackgroundExpression patterns of many laticifer-specific gens are closely correlative with rubber yield of Hevea brasiliensis (para rubber tree). To unveil the mechanisms underlying the rubber yield, transcript levels of nine major latex metabolism-related genes, i.e., HMG-CoA synthase (HMGS), HMG-CoA reductase (HMGR), diphosphomevalonate decarboxylase (PMD), farnesyl diphosphate synthase (FPS), cis-prenyltransferase (CPT), rubber elongation factor (REF), small rubber particle protein (SRPP), dihydroxyacid dehydratase (DHAD) and actin depolymerizing factor (ADF), were dertermined, and the relationship between rubber yield with their expression levels was analysed.ResultsExcept HbHMGR1, HbPMD and HbDHAD, most of these genes were predominantly expressed in latex, and bark tapping markedly elevated the transcript abundance of the analyzed genes, with the 7th tapping producing the greatest expression levels. Both ethephon (ETH) and methyl jasmonate (MeJA) stimulation greatly induced the expression levels of the examined genes, at least at one time point, except HbDHAD, which was unresponsive to MeJA. The genes’ expression levels, as well as the rubber yields and two yield characteristics differed significantly among the different genotypes examined. Additionally, the latex and dry rubber yields increased gradually but the dry rubber content did not. Rubber yields and/or yield characteristics were significantly positively correlated with HbCPT, HbFPS, HbHMGS, HbHMGR1 and HbDHAD expression levels, negatively correlated with that of HbREF, but not significantly correlated with HbPMD, HbSRPP and HbADF expression levels. In addition, during rubber production, significantly positive correlations existed between the expression level of HbPMD and the levels of HbREF and HbHMGR1, between HbSRPP and the levels of HbHMGS and HbHMGR1, and between HbADF and HbFPS.ConclusionsThe up-regulation of these genes might be related to the latex production of rubber trees under the stress of bark tapping and latex metabolism. The various correlations among the genes implied that there are differences in their synergic interactions. Thus, these nine genes might be related to rubber yield and yield-related traits in H. brasiliensis, and this work increases our understanding of their complex functions and how they are expressed in both high-and medium-yield rubber tree varieties and low-yield wild rubber tree germplasm.
Highlights
Expression patterns of many laticifer-specific gens are closely correlative with rubber yield of Hevea brasiliensis
HbHMGS, HbFPS, HbCPT, HbREF, HbSRPP and HbADF were strongly expressed in latex tissue (Fig. 1), with values of 20.33, 5.54, 10.90- and 25.77-fold (HbHMGS), 2.39, 5.39, 3.64- and 5.89-fold (HbFPS), 3.13, 8685.16, 17,256.19- and 18.26-fold (HbCPT), 125.09, 52.96, 158.39- and 79.81-fold (HbREF), 4.46, 5.03, 3.27- and 2.72-fold (HbSRPP) and 5.90, 5.23, 2.55- and 4.79-fold (HbADF) those in leaves, female flowers, male flowers and bark, respectively (P < 0.01)
The HbHMGS, HbFPS and HbADF expression levels were greatest in the latex, with levels 1.54, 83.00, 5.25, 1.38, 1.38 and 22.15 times (P < 0.01) those of HbHMGR1, HbPMD, HbCPT, HbREF, HbSRPP, and HbDHAD, respectively
Summary
Expression patterns of many laticifer-specific gens are closely correlative with rubber yield of Hevea brasiliensis (para rubber tree). MVA is sequentially phosphorylated and ATP-dependently decarboxylated to form IPP [9,10,11] In this second step of the MVA pathway involving the synthesis of IPP, acetoacetyl-CoA and acetyl-CoA are aldol-condensed to HMG-CoA by HMG-CoA synthase (HMGS, EC 2.3.3.10), and HMG-CoA is further converted to MVA by HMG-CoA reductase (HMGR, EC 1.1.1.34). Rubber elongation factor (REF) is required for different prenyltransferases from broad sources to add a number of cis-IPP molecules to rubber chains [18] In both large and small rubber particles, REF and small rubber particle protein (SRPP) form a dense proteolipidic monomembrane with the lipid monolayer that contributes to the colloidal stability of latex [19]
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