Transfer RNA Aspartic Acid Methyltransferase 1 (TRDMT1/DNMT2) Regulates Plant Development and Gene Expression in the Moss Physcomitrium patens.

TRDMT1/DNMT2 is a unique 5-methylcytosine methyltransferase that utilizes the catalytic mechanism of a typical DNA methyltransferase to methylate cytosines in tRNAs. It is known to be involved in diverse physiological regulatory processes such as protein synthesis, immune response, stress and gene expression regulation. While its biological roles have been well studied in animal systems, its cellular functions in land plants have been poorly understood. This study aims to gain deeper insight into regulatory roles of TRDMT1/DNMT2 in the moss Physcomitrium patens. We previously reported that TRDMT1/DNMT2 plays a crucial role in stress tolerance in P. patens. In the present study we generated TRDMT1/DNMT2-disruptant lines (ppdnmt2fl) by deleting the catalytic motifs I to VII encoding genomic region. Phenotypic characterization showed developmental transitions to be affected in ppdnmt2fl. RNA bisulphite sequencing revealed C38 methylation in tRNAAsp(GTC) to be affected similar to Arabidopsis and non-plant species. Interestingly, methylation at additional sites (C48, C49) in tRNAAsp(GTC) were also observed to be affected in P. patens. Polysome profiling and genome-wide proteome analysis showed reduced association of translatable mRNAs with polysomes and differential protein accumulation in ppdnmt2fl. Transcriptome analysis and integration of the omics data (proteome and transcriptome) showed expression of housekeeping genes to be deregulated at transcript and protein levels. The work presented in this study highlights the role of TRDMT1/DNMT2 in maintaining physiological and biochemical homeostasis in P. patens. This molecular attribute underlies stress resilience of this early land plant and possibly contributed in its adaptation to terrestrial habitats during plant evolution.