Abstract
Nitrate is a major nitrogen source for plants. We have identified and characterized eight nitrate transport genes (PpNRT2;1-PpNRT2;8) from the moss Physcomitrella patens, which is amenable to homologus recombination. Although its expression level is only 3-6% of total NRT2 expression during steady-state growth with nitrate, PpNRT2;5 is unique among the moss NRT2s in that it is induced quickly when protonemata is transferred from ammomium-containing medium to nitrate- or nitrite-containing medium and that it requires nitrate or nitrite for its expression. PpNRT2;5-disrupted mutant, ΔNRT2;5, grew normally on nitrate-containing medium. However, the activities of nitrate or nitrite uptake of ΔNRT2;5 was lower and was induced slower than in wild-type after transfer of ammonium-grown protonemata to media containing low concentrations of nitrate or nitrite. Our data suggest that PpNRT2;5 has an important role in the initial phase of induction of nitrate/nitrite assimilating activity.
