Iron availability regulates ammonium toxicity by modulating Jasmonate biosynthesis and signaling

Plants adapt to changing environmental conditions by adjusting their growth physiology. Nitrate (NO3-), and ammonium (NH4+) are the major inorganic nitrogen forms for plant uptake. However, high NH4+ inhibits plant growth and roots undergo striking changes such as inhibition of cell expansion and division thus, leading to reduced root elongation. In this work, we show that high NH4+ modulate nitrogen metabolism and root developmental physiology by inhibiting iron (Fe) dependent Jasmonate (JA) signaling and response in Arabidopsis thaliana. Transcriptomic data suggests that NH4+ availability regulates Fe and JA-responsive genes. High NH4+ levels lead to enhanced root Fe accumulation which in turn impairs nitrogen balance and growth by suppressing JA biosynthesis and signaling response. By integrating pharmacological, physiological, and genetic experiments, the study elucidates the involvement of NH4+ and Fe-derived responses in regulating root growth and nitrogen metabolism through modulation of the JA pathway during NH4+ stress. The JA signaling transcription factor, MYC2 directly binds with the promoter of the nitrate transporter gene, NRT1.1, and represses it to optimize NH4+/Fe-JA balance for plant adaptation during NH4+ stress.