The Arabidopsis nitrate transporter <scp>NRT</scp>2.5 plays a role in nitrate acquisition and remobilization in nitrogen‐starved plants

<jats:title>Summary</jats:title><jats:p>Nitrogen is a key mineral nutrient playing a crucial role in plant growth and development. Understanding the mechanisms of nitrate uptake from the soil and distribution through the plant in response to nitrogen starvation is an important step on the way to improve nitrogen uptake and utilization efficiency for better growth and productivity of plants, and to prevent negative effects of nitrogen fertilizers on the environment and human health. In this study, we show that Arabidopsis <jats:styled-content style="fixed-case">NITRATE TRANSPORTER</jats:styled-content> 2.5 (<jats:styled-content style="fixed-case">NRT</jats:styled-content>2.5) is a plasma membrane‐localized high‐affinity nitrate transporter playing an essential role in adult plants under severe nitrogen starvation. <jats:italic>NRT2.5</jats:italic> expression is induced under nitrogen starvation and <jats:italic><jats:styled-content style="fixed-case">NRT</jats:styled-content>2.5</jats:italic> becomes the most abundant transcript amongst the seven <jats:italic><jats:styled-content style="fixed-case">NRT</jats:styled-content>2</jats:italic> family members in shoots and roots of adult plants after long‐term starvation. <jats:styled-content style="fixed-case">GUS</jats:styled-content> reporter analyses showed that <jats:italic><jats:styled-content style="fixed-case">NRT</jats:styled-content>2.5</jats:italic> is expressed in the epidermis and the cortex of roots at the root hair zone and in minor veins of mature leaves. Reduction of <jats:italic><jats:styled-content style="fixed-case">NRT</jats:styled-content>2.5</jats:italic> expression resulted in a decrease in high‐affinity nitrate uptake without impacting low‐affinity uptake. In the background of the high‐affinity nitrate transporter mutant <jats:italic>nrt2.4</jats:italic>, an <jats:italic>nrt2.5</jats:italic> mutation reduced nitrate levels in the phloem of N‐starved plants further than in the single <jats:italic>nrt2.4</jats:italic> mutants. Growth analyses of multiple mutants between <jats:italic><jats:styled-content style="fixed-case">NRT</jats:styled-content>2.1</jats:italic>,<jats:italic> <jats:styled-content style="fixed-case">NRT</jats:styled-content>2.2</jats:italic>,<jats:italic> <jats:styled-content style="fixed-case">NRT</jats:styled-content>2.4</jats:italic>, and <jats:italic><jats:styled-content style="fixed-case">NRT</jats:styled-content>2.5</jats:italic> revealed that <jats:styled-content style="fixed-case">NRT</jats:styled-content>2.5 is required to support growth of nitrogen‐starved adult plants by ensuring the efficient uptake of nitrate collectively with <jats:styled-content style="fixed-case">NRT</jats:styled-content>2.1, <jats:styled-content style="fixed-case">NRT</jats:styled-content>2.2 and <jats:styled-content style="fixed-case">NRT</jats:styled-content>2.4 and by taking part in nitrate loading into the phloem during nitrate remobilization.</jats:p>