SU(VAR)3-9 like histone methyltransferases control heterochromatic domains in 
eukaryotes. In Arabidopsis, 10 SUVH genes encode SU(VAR)3-9 homologues where 
SUVH1, SUVH2 and SUVH4 (KRYPTONITE) represent distinct subgroups of SUVH genes. 
Loss of SUVH1 and SUVH4 causes weak reduction of heterochromatic histone H3K9 
dimethylation, whereas in SUVH2 null plants mono- and dimethyl H3K9, mono- and 
dimethyl H3K27, and monomethyl H4K20, the histone methylation marks of 
Arabidopsis heterochromatin are significantly reduced. Like animal SU(VAR)3-9 
proteins SUVH2 displays strong dosage-dependent effects. Loss of function 
suppresses, whereas overexpression enhances, gene silencing, causes ectopic 
heterochromatization and significant growth defects. Furthermore, modification 
of transgene silencing by SUVH2 is partially transmitted to the offspring 
plants. This epigenetic stability correlates with heritable changes in DNA 
methylation. Mutational dissection of SUVH2 indicates an implication of its 
N-terminus and YDG domain in directing DNA methylation to target sequences, a 
prerequisite for consecutive histone methylation. Gene silencing by SUVH2 
depends on MET1 and DDM1, but not CMT3. In Arabidopsis, SUVH2 with its histone 
H3K9 and H4K20 methylation activity has a central role in heterochromatic gene 
silencing.