4.8 Article

Nitrate-Dependent Control of Shoot K Homeostasis by the Nitrate Transporter1/Peptide Transporter Family Member NPF7.3/NRT1.5 and the Stelar K+ Outward Rectifier SKOR in Arabidopsis

Journal

PLANT PHYSIOLOGY
Volume 169, Issue 4, Pages 2832-2847

Publisher

AMER SOC PLANT BIOLOGISTS
DOI: 10.1104/pp.15.01152

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Funding

  1. Studienstiftung des Deutschen Volkes
  2. China Scholarship Council
  3. Deutsche Forschungsgemeinschaft [Forschergruppe FOR 948, WI1728/14-2, KU715/10-2]

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Root-to-shoot translocation and shoot homeostasis of potassium(K) determine nutrient balance, growth, and stress tolerance of vascular plants. To maintain the cation-anion balance, xylem loading of K+ in the roots relies on the concomitant loading of counteranions, like nitrate (NO3-). However, the coregulation of these loading steps is unclear. Here, we show that the bidirectional, low-affinity Nitrate Transporter1 (NRT1)/Peptide Transporter (PTR) family member NPF7.3/NRT1.5 is important for the NO3--dependent K+ translocation in Arabidopsis (Arabidopsis thaliana). Lack of NPF7.3/NRT1.5 resulted in K deficiency in shoots under low NO3- nutrition, whereas the root elemental composition was unchanged. Gene expression data corroborated K deficiency in the nrt1.5-5 shoot, whereas the root responded with a differential expression of genes involved in cation-anion balance. A grafting experiment confirmed that the presence of NPF7.3/NRT1.5 in the root is a prerequisite for proper root-to-shoot translocation of K+ under low NO3- supply. Because the depolarization-activated Stelar K+ Outward Rectifier (SKOR) has previously been described as a major contributor for root-to-shoot translocation of K+ in Arabidopsis, we addressed the hypothesis that NPF7.3/NRT1.5-mediated NO3- translocation might affect xylem loading and root-to-shoot K+ translocation through SKOR. Indeed, growth of nrt1.5-5 and skor-2 single and double mutants under different K/NO3- regimes revealed that both proteins contribute to K+ translocation from root to shoot. SKOR activity dominates under high NO3- and low K+ supply, whereas NPF7.3/NRT1.5 is required under low NO3- availability. This study unravels nutritional conditions as a critical factor for the joint activity of SKOR and NPF7.3/NRT1.5 for shoot K homeostasis.

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