Читать книгу Biotechnology of Fruit and Nut Crops - Группа авторов - Страница 141

The occurrence of the mantled variant phenotype in the oil palm is associated with a reduction in the level of global DNA methylation (Jaligot and Rival, 2015). To explore possible relationships between DNA methylation and accumulation of DNA-(cytosine-5) methyltransferase (DNMT) transcripts, the full-length coding sequences corresponding to three different DNMT families in oil palm, namely the MET, CMT and DRM classes, have been isolated and characterized (Rival et al., 2008). The corresponding genes were designated as EgMET1, EgCMT1 and EgDRM1, and encode predicted polypeptides of 1543, 925 and 591 amino acid residues, respectively. Expression of oil palm DNMTs was compared between normal and variant calluses and inflorescence tissues using quantitative reverse-transcription PCR. A consistent increase in transcript levels of EgMET1 and EgCMT1 was found in variant fast-growing calluses relative to nodular-compact calluses. Nodular-compact calluses give rise to c.5% of abnormal regenerants, whereas fast-growing calluses generate 95% of ‘mantled’ palms in their clonal offspring and were previously demonstrated as having markedly hypomethylated DNA. In immature abnormal inflorescences only EgMET1 transcript levels were increased, while no changes in relative abundance of the EgCMT1 or EgDRM1 transcripts were observed. Therefore, the genome-wide hypomethylation previously described in mantled material cannot be explained by a decrease in expression levels of the de novo or maintenance DNMTs, a paradox which has been previously reported in tumour cells, where there is evidence for global hypomethylation of DNA.