Metabolism Plasticity on Account of <i>Aspartate aminotransferase</i> 10 Promotes Poplar Growth under Altered Nitrogen Regimes

Improving poplar productivity across a wide spectrum of nitrogen conditions is a primary objective in poplar breeding. In this research, we engineered transgenic poplars to overexpress the <i>aspartate aminotransferase 10</i> (<i>AspAT10</i>) gene. The results showed that these transgenic plantlets significantly outperformed the wild-type control in terms of growth under both nitrogen-poor and nitrogen-rich conditions, exhibiting increased biomass, height, and root development. This improvement was linked to changes in internal nitrogen pools (including NO₃^-, NH₄⁺, and total free amino acids) and sugar content. In line with the metabolic results, notable alterations in genes related to nitrogen and carbon metabolism as well as hormone signaling pathways were identified. Our findings highlight the versatile role of <i>AspAT10</i> in regulating poplar's adaptation to variable nitrogen availability, attributed to the reversible nature of its catalytic reaction, which allows for the flexible reprogramming of nitrogen and carbon metabolism to align nitrogen supply with plant demand.