Résumé
Epigenetics is the study of heritable changes in gene function that occur without a change in the DNA sequence. In recent years, this field has attracted much attention as more epigenetic controls of gene activities are being discovered. Such controls involve a complex interplay of DNA methylation, histone modifications, and RNA-mediated pathways from non-coding RNAs, notably silencing RNA (siRNA) and microRNA (miRNA). In plants, although epigenetic mechanisms help to protect cells from parasitic elements, this defence can complicate the genetic engineering process through transcriptional gene silencing. Furthermore, these phenomena have economic relevance, for example, in somaclonal variation: a genetic and phenotypic variation among clonally propagated plants from a single donor genotype. The loss of phenotypic fidelity is now a major impediment to the development of large scale propagation of plants through in vitro processes such as somatic embryogenesis. Examples of aberrant phenotypes in regenerated plants include abnormal leaf structures and variant floral morphology, both organs being of paramount importance for applications in horticulture and/or agriculture. Changes in DNA methylation have been hypothesised playing a key role in the mechanism underlying tissue-culture induced changes. Indeed, studies of both global methylation levels and the methylation of specific sites show that variation in DNA methylation occurs frequently during growth in tissue culture. In vitro plant regeneration, like somatic embryogenesis, bypasses the normal developmental process of fertilisation and plant development, thus potentially resulting in the instability of epigenetic patterns. The large-scale clonal propagation of oil palm (Elaeis guineensis Jacq.) is being hampered by the occurrence of the mantled somaclonal variation. Indeed, this abnormality which presents a homeotic-like conversion of male floral organs into carpelloid structures, hampers oil production since the supernumerary female organs are either sterile or produce fruits with poor oil yields. Beyond its primary interest in the search for discriminating markers against an economically crippling phenotype, the study of the mantled abnormality also provides a unique opportunity to investigate the regulation of reproductive development in a perennial tropical plant. The present interest on food and energy security as well as the concerns raised by the possibility of climate change further stress the need for a global comprehension of how crop plants react to their fluctuating environment and how their productivity can be affected. (Texte intégral)