Somaclonal variation in oil palm (Elaeis guineensis Jacq.):: the DNA methylation hypothesis

The occurrence of somaclonal variants (ca 5%) among populations of somatic embryo-derived oil palms (Elaeis guineensis Jacq.) currently hampers the scaling-up of clonal plant production. In order to investigate the relationship between the ''mantled' somaclonal variant and possible alterations in genomic DNA methylation rate, two complementary approaches have been used. HPLC quantification of relative amounts of 5-methyl-deoxycytidine has shown that global methylation in leaf DNA of abnormal regenerants is 0.5-2.5% lower than in their normal counterparts (20.8% vs 22%, respectively). When comparing nodular compact calli and fast growing calli, yielding respectively 5% and 100% of "mantled'' plantlets, this decrease was up to 4.5% (from 23.2 to 18.7%). An alternative method, the SssI-methylase accepting assay, based on the enzymatic saturation of CG sites with methyl groups, gave convergent results. This work demonstrates that a correlation exists between DNA hypomethylation and the ''mantled" somaclonal variation in oil palm.