|dc.description.abstract||DNA methylation plays an important role in regulating plant development and is associated with the silencing of gene expression. Earlier studies of mammalian and vertebrate cells have shown that there are several methyl-CpG-binding (MBD) proteins that bind methylated DNA, and in cooperation with histone deacetylases (HDAC) and chromatin remodelling complexes lead to chromatin remodelling and gene silencing. In plants, DNA methylation is seen as a key regulator of imprinting of paternal genomes, transition from vegetative to reproductive growth, control of transposon activity and transgene silencing.
However, the way by which the DNA methylation code is interpreted into functional state has not been clarified. There have been many suggestions, and recently proteins with domains similar to MBD have been identified. A PSI-BLASTN screenings of Arabidopsis genome resulted in twelve genes encoding the MBD proteins, namely AtMBD1-AtMBD12 that are, based on their extended sequence similarity, classified into three different subgroups. Further, the RT-PCR analysis on all twelve genes showed that at least ten of the AtMBD genes are active genes (Berg et al., 2003).
With an aim to find their functions and expression patterns in plants, we have based our research on three genes encoding AtMBD proteins, namely AtMBD4, AtMBD8 and AtMBD11. Information provided studying these genes as the representatives for different subgroups creates a basis for further characterization of respective subclasses.
In order to investigate the expression pattern in more detail, AtMBD promoter-GUS (AtMBD::GUS) constructs have been made for these three AtMBD genes. The results observed varied according to the different plant lines and also according to the plant tissue analysed, meaning that some tissues/plant lines possessed more/less of the expressed gene compared to the other. The common feature of all plants analyzed was expression in floral organs.
To examine the biological function of plant MBD proteins, the expression level of the three genes was reduced performing the technique of RNA interference (RNAi). Transgene plant lines for two of the genes, AtMBD8 and AtMBD11, displayed a variety of phenotypic effects including aerial rosettes, serrated leaves, and abnormal position of flowers, reduced fertility and also late flowering. These findings correlate with phenotypes found in plants with reduced expression of genes involved in chromatin remodelling and transgene silencing, giving the support to our initial theory.||nor