Effect of different DNA demethylating agents on in vitro cultures of peach rootstock GF 677

Abstract

The appearance of somaclonal variability induced by in vitro cultivation is relatively frequent and, in some cases, provides a valuable source of new phenotypes suitable for crop improvement. Numerous studies have confirmed that these changes can be explained by alterations of DNA methylation. Interestingly, a group of chemical compounds termed 'demethylating agents' (DMT agents) enable artificial changes to be made in the DNA methylation state. Thus, these agents are theoretically able to induce new phenotypes or more favourable properties. The objective of the present study was to verify suitable conditions for the application of different DMT agents within in vitro protocols for micropropagation using the stone fruit rootstock GF 677 as an example. The impact of these agents on the properties of plant regenerants was evaluated, and their DNA methylation state was controlled by using an AFLP protocol based on a restriction endonuclease that differed in its sensitivity to methylated cytosines. Moreover, the effect of newly synthesised derivates was compared with that of conventional compounds with a well-documented DNA-demethylating impact. Based on the results, the suitable concentration for treatment by a DMT agent was established as approximately 50 μM. Promising results were generated using a combination of DMT agents with different mechanisms of action, such as azacytidine and dihydroxypropyladenine; under these conditions, probable synergy between methyltransferase interception by the cytosine analogue and interruption of methyl group donation by dihydroxypropyladenine significantly changed the DNA methylation state of treated plants. Regarding newly synthesised compounds, the 5,6-dihydro-5-azacytosine nucleoside showed the most promising results, which can likely be explained by its higher stability in the media used for in vitro cultivation.