Abstract
Plant nitrate transporters (NRTs) are classified into NRT1 and NRT2. NRT2 transporters play major roles in high-affinity nitrate uptake. Plants usually have several NRT2 molecular species, some of which require NAR2 for its expression and function. 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 higher affinity for nitrate than NRT2;3, whereas no such functional differentiation is known for NAR2. Functional relationships between the NRT2 and NAR2 molecular species is also unknown. To analyze the function of each NAR2 species, we constructed single and double mutants of NAR2;1 and NAR2;2 . Analysis of the expression of NRT2;3 protein in the mutants using anti-NRT2;3 antibody showed that the NRT2;3 protein was stably expressed in a single mutant of NAR2;1 and NAR2;2. By contrast, the protein was not detectable in a double mutant of NAR2;1 and NAR2;2, indicating that NAR2;3 cannot support expression of the NRT2;3 protein. We are currently trying to further clarify the function of NAR2;1 and NAR2;2 and to construct a NAR2;3 knockout mutant.
