DNA methylation is a key epigenetic process that plays a crucial role in silencing transposons and maintaining genome integrity. Over time, the substrates for DNA methylation have evolved differently across species. In plants, two enzymes, chromomethylase3 (CMT3) and CMT2, are responsible for methylating different DNA sequences: CHG and CHH, respectively.
However, it has not been clear how these two methyltransferases evolved to recognize different substrates. A recent study showed that CMT2 originated from an ancient duplication of CMT3 in flowering plants. The absence of a specific arginine residue in CMT2, which is essential for recognizing CHG in CMT3, explains why CMT2 does not methylate CHG in most flowering plants.
"By engineering a V1200R mutation, we restored both CHG and CHH methylation in Arabidopsis plants lacking CMT2 and CMT3, demonstrating that CMT2 has lost its ability to methylate CHG during evolution." Furthermore, CMT2 has developed a long, unstructured amino terminus that is critical for the stability of the protein, especially under heat stress, and is adaptable enough to accommodate natural mutations.
"This research provides new insights into how chromomethylases have diverged to mediate context-specific DNA methylation in plants and offers a deeper understanding of the evolution and function of DNA methylation."
Jianjun Jiang et al., Substrate specificity and protein stability drive the divergence of plant-specific DNA methyltransferases.Sci. Adv.10,eadr2222(2024).DOI:10.1126/sciadv.adr2222
Source: Science Advances