Abstract
Plants have evolved a set of responses to adapt to nitrogen (N)-limited conditions. However, little is known about the molecular basis of these responses. Here we characterized AtNRT2.4, which encodes a putative high-affinity nitrate transporter, as a candidate gene involved in plant adaptation to N-limitation. AtNRT2.4 is preferentially expressed in lateral root epidermal cells of N-limited plants. Furthermore, transgenic plants expressing AtNRT2.4-GFP fusion protein demonstrated that AtNRT2.4-GFP is localized in distal side of the epidermal cell, implying that AtNRT2.4 plays a role in nitrate-acquisition under N-limiting conditions. Thus, to evaluate whether AtNRT2.4 can transport nitrate, the Xenopus laevis oocyte system was employed. AtNRT2.4 mRNA-injected oocytes imported significantly more nitrate than water-injected controls, showing that AtNRT2.4 functions as a nitrate transporter. Furthermore, we characterized T-DNA insertional mutants. The mutant showed reduction in nitrate uptake compared with WT at low nitrate concentration (< 50 μM). Together, these results indicate that AtNRT2.4 is involved in adaptation to low-N conditions in Arabidopsis.
