Résumé
This 2006 annual report by the IRRDB biotechnology group has been expanded to coyer operations being conducted on Hevea in organizations other than rubber research institutes. The organizations involved are BGRICAS in China (Beijing Gene Research Institute of the Chinese Academy of Sciences), !RD and UBP-INRA in France, UKM in Malaysia, the universities of Mahidol (MU) and Kasetsart (KU) in Thailand, and the' University of Santa Cruz in Brazil (UESC). Alongside the disciplines usually covered, strategies combining several biotechnologies are proposed and a major surge in transgenesis and genomics has led to new functions being identified and analysed. In vitro culture research is still very active.Work has been resumed on microcuttings. The low multiplication rates for RRIC and RRISL clones have led researchers at RRISL to rejuvenate the clones ·by microbudding embryos onto young I-month-old seedling rootstocks. CIRAD, mRIEC arid IRRI are currently studying the feasibility of propagating rootstock clones by microcuttings. Somatic embryogenesis remains the preferred technique for mass propagation of rubber trees ·on their own roots, aIong with the development of transgenesis. Although sorne Sri Lankan and Malaysian clones (RRIM 2020) remain recalcitrant, routine production, of thousands of plants has been achieved by CATAS, CIRAD and Michelin. Over several years, CIRAD has been developing a technique for the cyropreservation of embryogenic callus which is now being routinely used to conserve lines with high embryogenic potential. Plants genetically modified for endogenous functions or through foreign gene insertion are now regularly produced in Hevea. GFP (Green Fluorescent Protein) expression has been achieved at CIRAD to monitor the evolution of transgenic lines and eventually do away with antibiotic-based selection.Work is under way at CATAS and .CIRAD to improve tolerance of cold (HbCBFltranscriptioD factor) and oxidative stress (CuZnSOD) respectively. A'gene involved in rubber ti-ee growth has been introduced into transgenic plants at MRB,' al~ng with several foreign g~nes such as those encoding HP (human protamine);PHB· (bioplastic), and the ScFv4715 antibody. Molecular physiology work is focusing on latex production and resistance to diseases. j13eforehand, an interesting latex RNA extraction" technique at ambient temperature was published in 1.B.B. Methods. Sugar loading depends on transporters for which several genes have been isolated by the CATAS and UBP-INRA'teams~ Sorne researchers from MRB have discovered that the mevalonate pathway was probably not the only pathway for IPP (isopentenyl pyrophosphate) production. The DXPIMEP pathways would seem to ~e an alternative occurring in plasts. Six isoforms of DXPSynthase have been isolated and are undergoing characterizatjon. Interestingly, the possible involvement of FreyWyssling particles in IPP synthesis is proposed through this pathway. V-PPase (Vacuole pyrophosphatase) has been located on the membranes of rubber partîcles and lutoids by " researchers at CATAS. That enzyme would seem to catalyse the degradation of a byproduct of rubber biosynthesis, pyrophosphate acid. Following the demonstration of an activity destabilizing the rubber particles in bark extracts, analyses at MRB led to the discovery of a polymeric phenolic compound that would seem to play a crucial role in that phenomenon. Far upstream, studies on the biosynthesis and regulation of ethylene and jasmonate are being carried out at CATAS, CIRAD and IRRI to describe the molecular mechanisms controlled by those hormones affecting latex production and triggering TPD. Lastly, the HbMybl transcription factor involved in cell apoptosis regulation is being investigated at CATAS to determine its involvement in TPD. Among the recent developments in functional genomics,worth mentioning is the generation of nucleic sequence libraries for expressed sequence tags (EST) in latex (30,000 EST at CATAS, 20,000 EST at MRB