Transcript Profiling Provides Insights into the Molecular Mechanisms of Harvesting-activated Latex Regeneration in Virgin Rubber Trees

Abstract Background: Natural rubber, an important industrial raw material with wide applications, is harvested in the form of latex (cytoplasm of rubber-producing laticifers) from Hevea brasiliensis (para rubber tree) by the way of tapping, i.e. removing a slice of trunk bark by a special knife. In regularly tapped rubber trees, latex regeneration consists of one of the main yield-limiting factors for rubber productivity. Conspicuous stimulation on latex production for the first few tappings makes virgin (untapped before) rubber trees an ideal model to investigate the regulatory mechanisms of latex regeneration. To understand the underlying mechanisms, genome-wide transcript profiling was conducted with a silver-staining cDNA-AFLP technology against the latex samples for the first five tappings.Results: A total of 505 non-redundant differentially expressed (DE) transcript-derived fragments (TDFs) were identified, of which 217 were up-regulated, 180 down-regulated, and 108 bell type-regulated among the five tappings. About 72.5% of these DE-TDFs were functionally annotated, and classified into 11 functional categories, which were discussed with reference to harvesting-stimulated latex regeneration. The importance of sugar metabolism and rubber biosynthesis was highlighted, due to the fact that most of the DE-TDFs annotated in sucrose transport, sugar catabolism, glycolysis, tricarboxylic acid cycle and pentose-phosphate pathway and nine of the ten rubber biosynthesis pathway DE-TDFs were up-regulated by the tapping treatment. More than one tenth of the total DE-TDFs were randomly selected for expression validation by semi-quantitative RT-PCR, and 83.8% showed patterns consistent with their original cDNA-AFLP gel profiles. Moreover, quantitative RT-PCR analysis revealed an 89.7% consistency for the 29 latex-regeneration related DE-TDFs examined.Conclusions: In brief, our results indicate the tapping treatment incurs extensive physiological and molecular changes in the laticifers of virgin rubber trees. The vast numbers of tapping-responsive DE-TDFs identified here provide a basis for unravelling the gene regulatory network for latex regeneration in regularly harvested rubber trees.