Assessment of various strategies for the preservation of clonal genetic resources in oil palm (Elaeis guineensis Jacq.)

Three different approaches for the preservation of oil palm (Elaeis guineensis Jacq.) clonal genetic resources and their impacts on the induction of the « mantled » somaclonal variation were assessed. In vitro long term preservation of somatic embryos stock-cultures was studied : after a 5 year cultivation period, 75 % of clonal lines were still normal. Between 8 and 13 years of embryo cultures, half of the considered clonal lines were found to be « mantled ». Finally, 40 % were found to be normal over 15 years of in vitro conservation. Clonal conformity of ramets resulting from the re-cloning of somaplants depended, on one hand, on the floral status of the mother plant at the time of sampling and, on the other hand, on its origin. Re-cloning of abnormal regenerants led, in all cases, to 100 % abnormal offspring. The age of the ramet used as mother palm at the time of sampling was found to be critical for true-to-type regeneration. There is a high risk of obtaining variant regenerant palms if the clonal mother palm is sampled at nursery stage. Field observations carried out on palms originating from somatic embryos cryopreserved at -196 °C showed floral conformity rates comparable to those obtained from standard not-cryopreserved clonal palms, for 6 out of the 8 clonal lines studied. From the 2 remaining clonal lines, a few regenerant palms originating from standard batch were found to be « mantled », whereas those resulting from cryopreserved embryos were all normal. The assumption of changes in levels of genomic DNA methylation during preservation was discussed, together with the capacity of our cryopreservation protocol to select embryogenic cells which were only suited to trueto-type regeneration

Oil palm biotechnology: progress and prospects

Today, a range of biotechnological approaches, from somatic embryogenesis to biomolecular research, play an increasingly important role in breeding strategies for oil palm (Elaeis guineensis Jacq.). Clonal micropropagation. Methods of cloning by in vitro culture led to the development of a micropropagation technique for oil palm based on somatic embryogenesis which was tested at the pilot stage on elite genotypes, thus enabling the production of high oil yielding clones. This phase allowed the identification of limiting factors associated with scaling-up, with respect in particular to the scale of mass production required to meet the needs of planters and to the problem of ensuring genetic fidelity in the regenerated plant material. These two concerns led researchers to look further into the underlying physiological and/or molecular mechanisms involved in somatic embryogenesis and the somaclonal variation events induced by the in vitro cloning procedure. Structural and functional genomics. Marker-assisted breeding in oil palm is a long-term multi-stage project including: molecular analysis of genetic diversity in both E. guineensis and E. oleifera germplasms; large scale development of PCR-based microsatellite markers; and parallel development of three genome mapping and QTL detection projects studying key agronomic characters. Post-genomics. In order to tackle the problem of the mantled flowering abnormality, which is induced during the micropropagation process, studies of gene expression have been carried out in tissue cultures as a means of establishing an early clonal conformity testing procedure. It is important to assess what kind of methodology is the most appropriate for clonal conformity testing by comparing RNA, protein and DNA (PCR) based approaches. Parallel studies on genomic DNA methylation changes induced by tissue culture suggest that the latter may play an important role in the determination of the mantled abnormality. (Résumé d'auteur

Syndrome métabolique : quelle définition pour quel(s) traitement(s) ?

Le syndrome métabolique, asymptomatique, résulte de la prévalence élevée de l’obésité. Malgré l’intérêt scientifique croissant suscité par ce syndrome, notamment en raison du problème majeur de santé publique qu’il soulève, lié au vieillissement de la population et à l’évolution des modes de vie, ses mécanismes physiopathologiques ne sont pas élucidés, et sa définition comme ses critères diagnostiques encore non harmonisés. Malgré cette coexistence de plusieurs définitions qui compliquent son diagnostic, il est caractérisé par la conjonction de troubles, souvent modérés, d’origine glucidique, lipidique ou vasculaire, associés à une surcharge pondérale, qui vont agir en synergie, provoquer un diabète de type 2 et prédisposer à l’athérosclérose et à ses événements cliniques. La prévalence du syndrome métabolique, élevée quel que soit l’âge, est en forte progression chez les jeunes. Audelà des interventions hygiénodiététiques, la plupart des traitements actuels sont focalisés sur un seul facteur de risque, et ne satisfont pas réellement le besoin médical : certaines classes d’antidiabétiques, d’hypolipémiants ou d’antihypertenseurs ont prouvé leur efficacité en prévention secondaire, contre la survenue d’événements cardiovasculaires, mais dans leurs indications respectives, et non spécifiquement chez les patients présentant un syndrome métabolique. Cependant, pour que le syndrome métabolique puisse être une indication thérapeutique spécifique, il faudrait identifier ses mécanismes physiopathologiques, harmoniser sa définition, démontrer l’efficacité clinique de certaines molécules et, probablement, développer de nouvelles entités dotées d’un mécanisme d’action multimodal. Quelques nouvelles approches sont évoquées, qui pourraient constituer une avancée décisive parallèlement à certains résultats positifs obtenus dans les études Field et Proactive relatives à l’utilisation de modulateurs PPAR (récepteurs activés par les proliférateurs de peroxisomes)