IN-VITRO DNA METHYLATION BY WHEAT NUCLEAR CYTOSINE DNA METHYLTRANSFERASE - EFFECT OF PHYTOHORMONES

Cytosine DNA methyltransferases (MTases) were isolated from nuclei of wheat seedlings and germinating embryos. The MTases isolated from both sources were able to perform de novo and maintenance DNA methylations . The most purified MTase fraction showed the presence of one main 67- kDa protein (embryos) and of a 85-kDa protein (in seedlings) in SDS-PA GE. Some plant growth regulators (gibberellic acid A,, 6-benzylaminopu rine and fusicoccin) elevate by 30-65% the extent of in vitro DNA meth ylation by nuclear extracts with a maximal effect at 10(-6) M phytohor mone concentration. The same phytohormones do not increase the extent of in vitro DNA methylation by purified wheat MTase; rather they inhib it it at concentrations of 10(-4)-10(-5) M. Thus, DNA methylation in t he plant nucleus is controlled by phytohormones. The phytohormone effe ct may be mediated by other proteins in nuclear extracts.