Journal 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

Bohner, Anne, Rausch, Christine, Kunze, Reinhard, Zheng, Yue, von Wirén, Nicolaus, Drechsler, Navina, Nobmann, Barbara

2015

Overview

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.

• Publisher: American Society of Plant Biologists
• Subject: 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