The Arabidopsis Target of Rapamycin kinase regulates ammonium assimilation and glutamine metabolism

In eukaryotes, a target of rapamycin (TOR) is a well-conserved kinase that controls cell metabolism and growth in response to nutrients and environmental factors. Nitrogen (N) is an essential element for plants, and TOR functions as a crucial N and amino acid sensor in animals and yeast. However, knowledge of the connections between TOR and the overall N metabolism and assimilation in plants is still limited. In this study, we investigated the regulation of TOR in Arabidopsis (Arabidopsis thaliana) by the N source as well as the impact of TOR deficiency on N metabolism. Inhibition of TOR globally decreased ammonium uptake while triggering a massive accumulation of amino acids, such as Gln, but also of polyamines. Consistently, TOR complex mutants were hypersensitive to Gln. We also showed that the glutamine synthetase inhibitor glufosinate abolishes Gln accumulation resulting from TOR inhibition and improves the growth of TOR complex mutants. These results suggest that a high level of Gln contributes to the reduction in plant growth resulting from TOR inhibition. Glutamine synthetase activity was reduced by TOR inhibition while the enzyme amount increased. In conclusion, our findings show that the TOR pathway is intimately connected to N metabolism and that a decrease in TOR activity results in glutamine synthetase-dependent Gln and amino acid accumulation. Inhibition of the important nitrogen metabolism sensor and regulator Target of Rapamycin (TOR) kinase affects ammonium uptake, causing glutamine accumulation in a glutamine synthetase-dependent manner.

Automated summary

In eukaryotes, the target of rapamycin (TOR) kinase plays a crucial role in controlling cell metabolism and growth in response to nutrients and environmental factors. This study focused on investigating TOR in Arabidopsis and its regulation by nitrogen (N) source, as well as the impact of TOR deficiency on N metabolism. The results showed that TOR inhibition globally reduced ammonium uptake and led to the accumulation of amino acids, including glutamine (Gln), and polyamines. Furthermore, the study revealed that TOR inhibition decreased glutamine synthetase activity but increased its enzyme amount, suggesting a connection between TOR pathway and glutamine synthetase-dependent Gln accumulation.