Résumé
Epigenetics is the study of heritable changes in gene function that occur without a change in the DNA sequence. In plants, although epigenetic mechanisms help to protect cells from parasitic elements, this defense can complicate the genetic engineering process through transcriptional gene silencing. These phenomena have economic relevance in the case of somaclonal variation: a genetic and phenotypic variation among clonally propagated plants from a single donor genotype. In oil palm (Elaeis guineensis Jacq), approximately 5% of somatic embryo-derived palms show abnormalities in their floral development. The "mantled" variant phenotype offers a very interesting model, because somaclonal variation alters the expression of genes coding, directly or indirectly, for the flower structure, and DNA hypomethylation has already been clearly demonstrated in somaclonal variants. Methylation sensitive DNA markers have been investigated using MSAP and MS-RFLP techniques and the three different classes of DNA methyltransferases have been studied comparatively in normal and variant material. Differential display and microarray approaches are currently developed in order to provide a range of putative candidate genes displaying expression which might be regulated through DNA methylation and/or chromatin remodeling. We have identified floral homeotic genes of the "MADS box" transcription factor family which are affected by the chain of events resulting in the "mantled" abnormality. Our aim is to describe specific molecular events which could be used for the development of markers of epigenetic instability in plants. These markers will be integrated in a strategy aimed at the identification of in vitro treatments that are prone to generate epigenetic variability in somatic embryogenesis-based micropropagation processes.