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-PAGE. Some plant growth regulators (gibberellic acid A3, 6-benzylaminopurine and fusicoccin) elevate by 30-65% the extent of in vitro DNA methylation by nuclear extracts with a maximal effect at 10(-6) M phytohormone concentration. The same phytohormones do not increase the extent of in vitro DNA methylation by purified wheat MTase; rather they inhibit it at concentrations of 10(-4)-10(-5) M. Thus, DNA methylation in the plant nucleus is controlled by phytohormones. The phytohormone effect may be mediated by other proteins in nuclear extracts.