NRT1.1 involved in balance between NH4+ uptake and assimilation ($) (Plant Physiol)

Ammonium (NH₄⁺) is an inorganic nitrogen source that is the preferred source for some plant species (e.g., rice and tea) but can be toxic in high amounts. The nitrate transporter NRT1.1 is involved in mediating the effects of toxic NH₄⁺, as well as functioning in NO₃^– and auxin transport, NO₃^– signaling and stomatal movement. But the role of NRT1.1 in mediating NH₄⁺ toxicity is still unclear. Thus, Jian and colleagues used Arabidopsis mutants, genetic analyses and enzyme analyses to elucidate the role of NRT1.1 in NH₄⁺ mediation. Under (NH₄)₂SO₄ stress, NRT1.1 induced the expression of various NH₄⁺-related transporters and NH₄⁺ assimilation genes. High (NH₄)₂SO₄ caused wild-type plants to grow poorly compared to the NRT1.1 mutants. For wild-type Arabidopsis, treatment with (NH₄)₂SO₄ induced toxicity responses, such as ethylene synthesis and senescence. Under (NH₄)₂SO₄ stress, the NRT1.1 mutants showed a reduction in NH₄⁺ accumulation and an enhancement in NH₄⁺ assimilation. This paper describes that NH₄⁺ toxicity is related to a nitrate-independent signaling function of NRT1.1, resulting in altered NH₄⁺ accumulation and metabolism. (Summary by Julia Miller) Plant Physiology: 10.1104/pp.18.00410