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Regulation of genomic DNA methylation in oil palm (Elaeis guineensis Jacq) somaclonal variants

Rival A., Jaligot E., Beulé T., Finnegan J.. 2006. In : 8th International Congress of plant molecular biology, Adelaide, Australia, August 20 to 25, 2006. Book of abstracts. Adelaide : ISPMB, p. 45-45. International Congress of Plant Molecular Biology. 8, 2006-08-20/2006-08-25, Adelaide (Australie).

In oil palm (Elaeis guineensis Jacq), approximately 5% of somatic embryo-derived palms show homeotic changes in their floral development, involving an apparent feminisation of male parts in flowers of both sexes, called the "mantled" phenotype. Properties revealed in field trials (spatial and temporal heterogeneity, reversion of phenotype, non-Mendelian segregation) have led to the hypothesis of an epigenetic origin for the "mantled" variation. The variant phenotype is associated with reduced DNA methylation. DNA methylation patterns are established and maintained by DNA methyltransferases which catalyse the transfer of the methyl group from S-adenosylmethionine to the C-5 position in the pyrimidine ring of cytosine. We have recently isolated and characterised two different oil palm DNA methyltransferases, belonging to the METI and CMT3 families. Expression of oil palm METI and CMT3 has been compared in normal and variant calli from the same genotype using semi-quantitative RTPCR. Variant calli are reported to give rise to more than 95% "mantled" palms and they are characterised by a substantial DNA hypomethylation when compared to their normal counterparts. We found no difference in expression level of these two genes in normal and abnormal calli. The genome-wide hypomethylation previously described in "mantled" material cannot be explained by a decrease in expression levels of METI and CMT3 methyltransferases, a paradoxical result which has been already outlined in cancer research. The possible role of oil palm methyltransferase from the DRM family (de novo methylation of isolated C motifs) in the molecular determinism of somaclonal variation is currently under study and our research efforts will also focus on methylation status around target genes, including analogues in oil palm of MADS box genes governing flower structure. (Texte intégral)

Mots-clés : elaeis guineensis; méthylation; adn; expression des gènes; phénotype; variation génétique; huile de palme; transférase

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