AtTrm5a catalyses 1-methylguanosine and 1-methylinosine formation on tRNAs and is important for vegetative and reproductive growth in Arabidopsis thaliana.

Modified nucleosides on tRNA are critical for decoding processes and protein translation. tRNAs can be modified through 1-methylguanosine (m1G) on position 37; a function mediated by Trm5 homologs. We show that AtTRM5a (At3g56120) is a Trm5 ortholog in Arabidopsis thaliana. AtTrm5a is localized to the nucleus and its function for m1G and m1I methylation was confirmed by mutant analysis, yeast complementation, m1G nucleoside level on single tRNA, and tRNA in vitro methylation. Arabidopsis attrm5a mutants were dwarfed and had short filaments, which led to reduced seed setting. Proteomics data indicated differences in the abundance of proteins involved in photosynthesis, ribosome biogenesis, oxidative phosphorylation and calcium signalling. Levels of phytohormone auxin and jasmonate were reduced in attrm5a mutant, as well as expression levels of genes involved in flowering, shoot apex cell fate determination, and hormone synthesis and signalling. Taken together, loss-of-function of AtTrm5a impaired m1G and m1I methylation and led to aberrant protein translation, disturbed hormone homeostasis and developmental defects in Arabidopsis plants.

The 2'-O-methyladenosine nucleoside modification gene OsTRM13 positively regulates salt stress tolerance in rice.

Stress induces changes of modified nucleosides in tRNA, and these changes can influence codon-anticodon interaction and therefore the translation of target proteins. Certain nucleoside modification genes are associated with regulation of stress tolerance and immune response in plants. In this study, we found a dramatic increase of 2'-O-methyladenosine (Am) nucleoside in rice seedlings subjected to salt stress and abscisic acid (ABA) treatment. We identified LOC_Os03g61750 (OsTRM13) as a rice candidate methyltransferase for the Am modification. OsTRM13 transcript levels increased significantly upon salt stress and ABA treatment, and the OsTrm13 protein was found to be located primarily to the nucleus. More importantly, OsTRM13 overexpression plants displayed improved salt stress tolerance, and vice versa, OsTRM13 RNA interference (RNAi) plants showed reduced tolerance. Furthermore, OsTRM13 complemented a yeast trm13Δ mutant, deficient in Am synthesis, and the purified OsTrm13 protein catalysed Am nucleoside formation on tRNA-Gly-GCC in vitro. Our results show that OsTRM13, encoding a rice tRNA nucleoside methyltransferase, is an important regulator of salt stress tolerance in rice.