Abstract
In the moss Physcomitrella patens, we previously identified eight nitrate transporter genes (PpNRT2;1-PpNRT2;8), the respective function of which has remained to be determined. In this study, we disrupted PpNRT2;1, PpNRT2;3 and PpNRT2;5, each of which has distinct structural characteristics and gene expression profile, by target mutagenesis to yield the mutants ΔNRT2;1, ΔNRT2;3 or ΔNRT2;5, respectively. These mutants grew normally under nitrate-replete conditions. Unlike ΔNRT2;1 and ΔNRT2;5, however, ΔNRT2;3 showed higher nitrate uptake activity than WT in the low substrate concentration range (0-100 μM). The expression levels of the other NRT2 genes, particularly PpNRT2;1 and PpNRT2;2, were higher in ΔNRT2;3 than in WT. These data suggest that PpNRT2;3 has relatively low affinity for nitrate. PpNRT2;1 and PpNRT2;2 are presumably high affinity nitrate transporters. In WT, high-level expression of PpNRT2;3 seems to indirectly control other NRT2 genes through the glutamine-mediated feedback repression mechanism.
