Question: Which are the plant DNA (cytosine-5) methyltransferase families?

Context:
The topologies of the trees were overall congruent: four monophyletic groups corresponding to the four plant C5-MTase families were clearly distinguished. In addition, sequence analyses of the plant C5-MTase target recognition domain sequences were performed and phylogenetic trees were reconstructed showing that there is good conservation among but not within the plant C5-MTase families.
To determine the inheritance of DNA methyltransferase genes and their expression patterns we examined three major DNA methyltransferase families (MET1, CMT3 and DRM) from tobacco and the progenitor species.
The comparative investigation of transcription levels of different genes of cytosine DNA methyltransferase family MET (MET1, MET2a, MET2b, MET3) and their methylation patterns shows that there may exist some mechanisms defending the most actively transcribed gene MET1 of this family from methylation mediated silencing. In contrast to DRM2 gene we could not find any adenine methylated GATC sites in the MET1 gene.
Using the 1kb 3' terminal DNA fragment of the mouse methyltransferase cDNA as a probe and low stringent hybridisation conditions, a new potential methyltransferase (MTase) gene family was isolated from an Arabidopsis thaliana genomic DNA library.
The Dnmt3 family of de novo DNA methyltransferases has recently been characterized in animals. Here we describe DNA methyltransferase genes from both Arabidopsis and maize that show a high level of sequence similarity to Dnmt3, suggesting that they encode plant de novo methyltransferases. Relative to all known eukaryotic methyltransferases, these plant proteins contain a novel arrangement of the motifs required for DNA methyltransferase catalytic activity.
These results provide the first direct demonstration that DNA-METases of a higher eukaryote are encoded by a gene family.
Here we show that Arabidopsis DNA methyltransferase2 (AtDNMT2) is localized in nucleus and associates with histone deacetylation.
To explore possible relationships between DNA methylation level and accumulation of DNA-(cytosine-5) methyltransferase (DNMT) transcripts, the full-length coding sequences corresponding to three different DNMT families in oil palm, namely the MET, CMT, and DRM classes, have been isolated and characterized.
In Arabidopsis a SWI2/SNF2 chromatin remodeling factor-related protein DDM1 and a cytosine methyltransferase MET1 are required for maintenance of genomic cytosine methylation.
Relative to all known eukaryotic methyltransferases, these plant proteins contain a novel arrangement of the motifs required for DNA methyltransferase catalytic activity.
In the present study, the isolation and characterization of two distinct cDNAs that code for carrot DNA (cytosine-5)-methyltransferase (DNA-METase) are reported.
The Arabidopsis methylase has eight of the ten conserved sequence motifs found in prokaryote cytosine-5 methyltransferases and shows 50% homology to the murine enzyme in the methyltransferase domain.
As deduced form the DNA sequence this protein contains all conserved sequence motifs specific for the 5m cytosine MTases.

Answer: The plant DNA (cytosine-5)methyltransferases are classified into the families: MET, CMT, and the de novo DRM.
Exact answer: MET, CMT, DRM