The nitrate transporter NRT1.1 is involved in iron deficiency responses in Arabidopsis

Iron (Fe) deficiency strongly induces Fe-acquisition gene expression. The nitrate transporter NRT1.1, which functions as a dual-affinity nitrate transporter and nitrate signaling sensor, is involved in many nitrate-dependent responses. However, the regulation of plant responses to Fe deficiency by NRT1.1 has not been described. In this study, it is shown that NRT1.1 is down-regulated by Fe deficiency. The functional disruption of NRT1.1 enhanced resistance to Fe deficiency stress: after 10 d Fe starvation, the shoot chlorosis phenotype of the NRT1.1-deficient mutant chl1-5 was alleviated compared to the wild type (WT). Furthermore, the levels of IRT1, FRO2, and FIT transcripts were less induced in chl1-5 plants under Fe-deficient conditions. Less nitrate accumulated in chl1-5 plants compared to WT and nitrate reductase (NR) activity was significantly decreased in WT plants after 10 d Fe deficiency treatment but not in the mutant. We propose that the functional disruption of NRT1.1 helps Arabidopsis plants to better adapt to Fe deficiency stress, which is most likely explained in terms of a physiological mechanism by which the reduced amount of accumulated internal nitrate could to impair an FIT-dependent Fe deficiency signaling pathway via a feedback mechanism.