Ethylene signaling modulates Arabidopsis thaliana nitrate metabolism

Genetic analysis reveals a previously unknown role for ethylene signaling in regulating Arabidopsis thaliana nitrogen metabolism. Nitrogen (N) is essential for plant growth, and assimilation of soil nitrate (NO₃^-) and ammonium ions is an important route of N acquisition. Although N import and assimilation are subject to multiple regulatory inputs, the extent to which ethylene signaling contributes to this regulation remains poorly understood. Here, our analysis of Arabidopsis thaliana ethylene signaling mutants advances that understanding. We show that the loss of CTR1 function ctr1-1 mutation confers resistance to the toxic effects of the NO₃^- analogue chlorate (ClO₃^-), and reduces the activity of the nitrate reductase (NR) enzyme of NO₃^- assimilation. Our further analysis indicates that the lack of the downstream EIN2 component (conferred by novel ein2 mutations) suppresses the effect of ctr1-1, restoring ClO₃^- sensitivity and NR activity to normal. Collectively, our observations indicate an important role for ethylene signaling in regulating Arabidopsis thaliana NO₃^- metabolism. We conclude that ethylene signaling enables environmentally responsive coordination of plant growth and N metabolism.