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 fluctuating environmental nitrogen availability. However, potential genes modulating plant response to nitrate have yet to be characterized. Here, a poplar GATA transcription factor gene PdGNC was found to be greatly induced by low nitrate. Overexpressing PdGNC in poplar clone 717-1B4 (P. tremula x alba) significantly improved nitrate uptake, remobilization, and assimilation with higher nitrogen-use efficiency (NUE) and faster growth, particularly in a low nitrate condition. Conversely, CRISPR/Cas9-mediated poplar mutant gnc exhibited decreased nitrate uptake, relocation, and assimilation 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 use pathway genes PdNRT2.4b, PdNR, PdNiR, and PdGS2, leading to a significant increase in nitrate utilization in poplar. Expectedly, the enhanced NUE promoted the growth under low nitrate availability. Taken together, PdGNC plays an important role in regulation of NUE and growth by improving nitrate acquisition, remobilization, and assimilation in poplar, and our research provides a promising strategy for tree molecular breeding to improve productivity under nitrogen limitation.