Abstract
In Physcomitrella patens, we previously identified and characterized five NRT2 genes and three Nar2 genes that are supposedly involved in active nitrate transport. In this study, we identified three new NRT2 genes (PpNRT2;6, PpNRT2;7 and PpNRT2;8) by screening the genome database. The deduced proteins are similar to PpNRT2;5 in lacking the hydrophilic amino acid segment conserved in the N-terminal region of PpNRT2;1-PpNRT2;4. Nitrogen regulation of PpNRT2;6 and PpNRT2;7 was similar to that of PpNRT2;1-PpNRT2;4 and distinct from that of PpNRT2;5, which strictly requires nitrate or nitrite for expression and is not susceptive to negative feedback caused by nitrogen assimilation. In contrast to PpNRT2;5, PpNRT2;8 was negatively regulated by nitrate and nitrite. In nitrate-replete protonemata, the PpNRT2;3 transcript was the most abundant among the PpNRT2 transcripts, suggesting the principal role of PpNRT2;3 in nitrate uptake from medium.
