| Popis: |
The two main limiting factors of rubber yield are the duration of the latex flow, which is limited by coagulation process, and the potential to regenerate the lost latex between two tappings. Stimulation with ethylene can partially overcome them. We had shown that hevein, a lectin-likeprotein, induces latex coagulation by bringing together the rubber particles(RPS). The hevein-RPS bridging is mediated by N-Acetyl-D-glucosamine, andinvolves a 22 kDa receptor glycoprotein localized on the RPS surface. This process is inhibited by the removal of the sugar moiety of the receptor, through the action of exochitinase or hevamine (a chitinase-lysozynle). Wecould clone the cDNA encoding these proteins. Northem analysis showed that:1) Ethylene induced an over expression of the 4 genes in the latex:chitinase, hevamine, hevein and its receptor. The earlier and higherover-expression of the chitinases can explain the partial deglycosylation of the hevein receptor and the resulting delay in coagulation. 2) In given ecoclimatic condition, the level of expression of hevein, hevamine and chitinase in the latex is a clonal characteristic. It can discriminate the highest yielding clones with prolonged latex flow, from the lowest yielding ones (short latex flow). 3) Coagulation of latex within the laticifers of TAD trees is not due to an overexpression of hevein and/or underexpression of chitinase or hevamine. Glutamine Synthetase (GS), is early overexpressed after an ethylene treatment, and may be one of the limiting factor of latex regeneration. These studies may lead to the proposal of new tools (molecular markers) for rubber improvement and selection programs, as well as for the latex diagnosis of the laticifers physiological status in rubber plantation. Further, the knowledges acquired at the molecular level on rubber yield limiting factors, should be of great help to select the key targets for the future genetic engineering of the rubber tree. |
