Investigating the effects of a mammalian demethylase in plant species

DNA methylation is one of a variety of epigenetic modifications that occurs in plant and animal genomes. It consists of a methyl group added to a cytosine base within the DNA. The established main effect of DNA methylation is to affect the expression of genes and other genetic elements by influencing the likelihood of transcription, although it may also have other effects for example by affecting splicing in maize. The removal of methylation, DNA demethylation, is carried out differently in plants and animals. In this project, the catalytic domain of the mammalian demethylase enzyme TET3, which removes methylation, has been transformed into plants both to investigate the mechanism of TET3-mediated demethylation and identify genes in plants which are sensitive to methylation changes. It is shown that this can result in both hypo- and hypermethylation in plants and in the production of oxidative derivatives of TET3-mediated demethylation. Methylation changes caused by TET3 in plants could be inherited in the absence of the transgene. In tomato, TET3 produces a heritable phenotypic change in shoot architecture, resulting from the demethylation and activation of a tomato gene which has not previously been functionally characterised. Transformation of TET3 into tomato also resulted in defects in shoot apical meristem maintenance allowing investigation of the causes of this phenotype, which can cause production losses for the tomato industry. TET3 was silenced in tobacco and lettuce, suggesting that expression of this gene may have detrimental effects in some species.