Identification of methylation-sensitive DNA markers of somaclonal variation in oil palm [S28-22]

The methylation-sensitive amplification polymorphism (MSAP) technique is a powerful tool which combines the advantages of AFLP, which generates a large number of DNA markers per sample, and the sensitivity to C methylation, provided by the MspI/HpaII isoschizomeric restriction. It was used on different genotypes of somatic embryo-derived oil palms (Elaeis guineensis Jacq.) in order to identify methylation polymorphisms correlated to the "mantled" somaclonal variation. This epigenetic phenomenon is characterised by homeotic modifications in whorl three in flowers of both sexes. The methylation status of MspI/HpaII sites was compared between normal and abnormal regenerant palms in four sets composed of three individuals of four different phenotype. Overall, 64 selective primer combinations were used during this preliminary screening and they have generated 23 markers exhibiting a phenotype-specific methylation pattern, 20 of them reflecting an hypomethylation of CCGG sites in variant comparatively to normal palms. These differential patterns were further asserted by extending our test panel to 9 normal versus 9 abnormal palms leaves from variants. Eight of the putative markers exhibited a clear presence/absence distribution pattern between the two phenotypes. They were consecutively isolated and used as Southern blot probes in order to ascertain their discriminating ability. The sequencing of these markers revealed structural similarities to genes with known functions. The detected homologies suggest interesting hypotheses about the identity of the cellular mechanisms which regulation is affected in the context of the "mantled" somaclonal variation. We question the significance of these polymorphisms, all of them strictly restricted to a single clonal line, with respect to the detection of methylation polymorphisms linked to the expression of the "mantled" somaclonal variation. (Texte intégral