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

• Published in: Plant physiology (Bethesda) Vol. 169; no. 4; pp. 2832 - 2847
• Main Authors: Drechsler, Navina, Zheng, Yue, Bohner, Anne, Nobmann, Barbara, von Wirén, Nicolaus, Kunze, Reinhard, Rausch, Christine
• Format: Journal Article
• Language: English
• Published: United States American Society of Plant Biologists 01.12.2015
• Subjects: Anion Transport Proteins - genetics; Anion Transport Proteins - metabolism; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis - physiology; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Gene expression regulation; Gene Expression Regulation, Plant; Homeostasis; Ion Transport - genetics; Ion Transport - physiology; Leaves; MEMBRANES, TRANSPORT, AND BIOENERGETICS; Mutation; Nitrates; Nitrates - metabolism; Phenotypes; Plant Proteins - genetics; Plant Proteins - metabolism; Plant roots; Plant Roots - genetics; Plant Roots - metabolism; Plant Roots - physiology; Plant Shoots - genetics; Plant Shoots - metabolism; Plant Shoots - physiology; Plants; Potassium; Potassium - metabolism; Reverse Transcriptase Polymerase Chain Reaction; Shaker Superfamily of Potassium Channels - genetics; Shaker Superfamily of Potassium Channels - metabolism; Xylem; Xylem - genetics; Xylem - metabolism; Xylem - physiology; Yeasts
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.15.01152

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 thenrt1.5-5shoot, 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 ofnrt1.5-5andskor-2single 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.