Abstract
The NRT2 genes, which encode the transporters involved in nitrate uptake, comprise a small gene family in most plants. NRT2;3 is one of the eight NRT2 species in the moss Physcomitrella patens, in which NRT2;1-NRT2;4 are the major NRT2 components. Of the four major NRT2 species, NRT2;3 has significantly lower afinity for nitrate than the other three, and its mRNA comprises over 80% of the total NRT2 mRNA in protonemata grown under a high (10 mM)-nitrate conditions. The activity of NRT2;3 is regulated posttranslationally, without involving protein degradation. An S414A mutant of NRT2;3, in which one of the putative phosphorylation sites conserved in most plant NRT2 proteins was mutated, showed normal expression level of the NRT2;3 mRNA but accumulated no NRT2;3 protein, while an S507A mutant accumulated the NRT2;3 protein but was similar to the NRT2;3 deletion mutant in its high-level expression of the NRT2 genes other than NRT2;3. These results suggest that S414 is required for maturation or stabilization of the NRT2;3 protein whereas S507 is essential for the activity of NRT2;3. Characteristics of the S414D and S507D mutants will be also reported.
