The transcription factor GNC optimizes nitrogen use efficiency and growth by up-regulating the expression of nitrate uptake and assimilation genes in poplar.

ABSTRACT

Plants have evolved complex mechanisms to cope with the fluctuating environmental availability of nitrogen. However, potential genes modulating plant responses to nitrate are yet to be characterized. Here, a poplar GATA transcription factor gene PdGNC (GATA nitrate-inducible carbon-metabolism-involved) was found to be strongly induced by low nitrate. Overexpressing PdGNC in poplar clone 717-1B4 (P. tremula × alba) significantly improved nitrate uptake, remobilization, and assimilation with higher nitrogen use efficiency (NUE) and faster growth, particularly under low nitrate conditions. Conversely, CRISPR/Cas9-mediated poplar mutant gnc exhibited decreased nitrate uptake, relocation, and assimilation, combined with lower NUE and slower growth. Assays with yeast one-hybrid, electrophoretic mobility shift, and a dual-luciferase reporter showed that PdGNC directly activated the promoters of nitrogen pathway genes PdNRT2.4b, PdNR, PdNiR, and PdGS2, leading to a significant increase in nitrate utilization in poplar. As expected, the enhanced NUE promoted growth under low nitrate availability. Taken together, our data show that PdGNC plays an important role in the regulation of NUE and growth in poplar by improving nitrate acquisition, remobilization, and assimilation, and provide a promising strategy for molecular breeding to improve productivity under nitrogen limitation in trees.