Genome-Wide Identification and Expression Pattern Analysis of the DNA Methyltransferase Gene Family Revealed the DNA Methylation Response to Tapping in Rubber Tree

DNA methylation is an epigenetic modification that plays a crucial role in the regulation of gene expression, genome defense, and numerous biological processes. DNA methyltransferase (MTase) is the pivotal enzyme catalyzing the DNA methylation reaction. To explore the regulation mechanism of DNA methylation in rubber trees (<i>Hevea brasiliensis</i>), we identified 13 genome-wide MTase genes containing conserved structural domains of DNA methyltransferase based on the rubber tree reference genome. Through phylogenetic analysis, these genes were classified into four subfamilies: MET1, CMT, DRM, and DNMT2. A significant expansion of DNA methyltransferase genes was found in rubber trees, especially in the DRM subfamily. Notably, among the four members of the MET1 subfamily, only HbMET1-1 contains the complete UBA and RFD domains, suggesting its critical role in the function of MET1 in plants, while the other members may have developed different functions during evolution. Gene expression pattern analysis revealed that most DNA methyltransferases were specifically expressed at low levels in latex. However, following tapping from unharvested rubber trees, the expression levels of HbMTase genes are altered, and these alterations exhibit variability. Among them, HbMET1-1 and HbDRM2-1 exhibited a response to tapping stress, with their expression levels rapidly increasing after stress application and subsequently decreasing gradually. The expression levels of HbCMT3-1 and HbCMT3-2 continued to increase as the rubber tapping process progressed, which was consistent with the observed changes in HbMTase enzyme activity. These findings suggest that tapping, as a form of mechanical stress, affects the expression of particular genes. Through subcellular localization analysis, we found that HbDNMT2 is the only DNA methyltransferase located in the cytoplasm its expression level gradually decreases during the rubber tapping process. It is hypothesized that this gene activates a multitude of genes involved in the rubber biosynthesis pathway and participates actively in rubber biosynthesis. In conclusion, the comprehensive analysis of the structural characterization, conserved domains analysis, cis-regulatory elements, subcellular localization, expression profiling, and HbMTase enzyme activity detection provides critical insights into the functional characteristics of DNA methyltransferases in rubber trees and initially reveals the DNA methylation response in rubber tree tapping.