Abstract
Plant cells take up nitrate, one of the major nitrogen sources, via nitrate transporters (NRTs). Plant NRTs are classified into NRT1 and NRT2. The NRT2 proteins, which play a major role in nitrate uptake from the soil solution, require the NAR2 protein for expression of their activity. Physcomitrella patens has eight NRT2 species and three NAR2 species. Among the eight NRT2 species, NRT2;1, NRT2;2 and NRT2;4 are more closely related to one another than to NRT2;3, and have been shown to have higher affinity for nitrate than NRT2;3. By contrast, no such functional differentiation is known for the NAR2 proteins. In order to analyze the function of each NAR2 species, we attempted to construct Nar2 mutants by targeted mutagenesis and to analyze their phenotype. We obtained single and double mutants of Nar2;1 and Nar2;2, all of which grew normally in the medium containing 5 mM nitrate. On the other hand, no Nar2;3 knockout mutant has been isolated after repeated trials, suggesting that NAR2;3 is essential for Physcomitrella patens . We are currently trying to determine the function of the NAR2;1 and NAR2;2 proteins by detailed analysis of the phenotype of the respective mutants.
