Arabidopsis TRM5 encodes a nuclear-localised bifunctional tRNA guanine and inosine-N1-methyltransferase that is important for growth
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Modified nucleosides in tRNAs are critical for protein translation. N<sup>1</sup>-methylguanosine-37 and N<sup>1</sup>-methylinosine-37 in tRNAs, both located at the 3’-adjacent to the anticodon, are formed by Trm5. Here we describe <em>Arabidopsis thaliana AtTRM5</em> (At3g56120) as a Trm5 ortholog. <em>Attrm5</em> mutant plants have overall slower growth as observed by slower leaf initiation rate, delayed flowering and reduced primary root length. In <em>Attrm5</em> mutants, mRNAs of flowering time genes are less abundant and correlated with delayed flowering. We show that <em>AtTRM5</em> complements the yeast <em>trm5</em> mutant, and <em>in vitro</em> methylates tRNA guanosine-37 to produce N<sup>1</sup>-methylguanosine (m<sup>1</sup>G). We also show <em>in vitro</em> that AtTRM5 methylates tRNA inosine-37 to produce N<sup>1</sup>-methylinosine (m<sup>1</sup>I) and in <em>Attrm5</em> mutant plants, we show a reduction of both N<sup>1</sup>-methylguanosine and N<sup>1</sup>-methylinosine. We also show that AtTRM5 is localized to the nucleus in plant cells. Proteomics data showed that photosynthetic protein abundance is affected in <em>Attrm5</em> mutant plants. Finally, we show tRNA-Ala aminoacylation is not affected in <em>Attrm5</em> mutants. However the abundance of tRNA-Ala and tRNA-Asp 5’ half cleavage products are deduced. Our findings highlight the bifunctionality of AtTRM5 and the importance of the post-transcriptional tRNA modifications m<sup>1</sup>G and m<sup>1</sup>I at tRNA position 37 in general plant growth and development.
