Effects of ethylene stimulation on rubber biosynthesis genes expression in Hevea brasiliensis laticifers
2009
Ruderman, S. | Kongsawadworakul, P. | Viboonjun, U. | Mongkolporn, O. | Chrestin, H.
Ethrel, an ethylene releaser, is widely used in rubber estates to enhance latex yield production. However, stimulation induces a decrease in the latex dry rubber content (DRC). Our research focused on how ethylene might affect the expression of the genes involved in the rubber biosynthesis pathways. Kinetic effects of ethylene on untapped and 4 months-tapped trees of the PB217 rubber clone were studied, using 1/2S d2. Seven batches 3 trees were set-up: two batches for control (no stimulation) and 5 batches with 5% Ethrel treated for 4, 8, 16, 24 and 40 hours before the first tapping. The second tapping was performed 2 days later. The same experiment was performed on the same trees 4 months later. Latex total RNA were extracted and the cDNA were synthesized. Randomized complete Block Design with 3 replications was set-up for gene expression analysis by real time RT-PCR. Results showed that the genes involved in the isoprene unit synthesis through the mevalonate rubber biosynthesis pathway, were markedly down-regulated by ethylene from both the 1st and 2nd tapping of virgin and tapped trees. Only HMGR3 was up-regulated. The genes involved in polymerization of isoprene units into rubber molecules showed down-regulation by ethylene. In addition, the genes involved in isoprene unit synthesis through the DXP/MEP isoprenoids pathway such as DXPS and DXPR were also down-regulated by ethylene in both the 1st and 2nd tapping of virgin and tapped trees. Conversely, the invertase gene encoding the enzyme involved in the entry of glycolysis, which produces the carbon skeleton for the whole cell anabolism and rubber biosynthesis, was up-regulated by ethylene in both virgin and tapped trees. Ethylene stimulation might favor the whole latex cell cytoplasm regeneration through increase in primary metabolism, at the expense of rubber synthesis.
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