Abstract
The moss Physcomitrella patens has eight genes coding for the NRT2 nitrate transporters. Among the PpNRT2s, PpNRT2;1-PpNRT2;4 are the major NRT2 species in the protonemata, while the others are minor components. Although expression of all of the NRT2 genes is induced by nitrate and repressed by glutamine, preferential expression of PpNRT2;3 is observed in the protonemata grown under nitrate-sufficient conditions. On the other hand, protonemata incubated in nitrogen-free medium expressed PpNRT2;1, PpNRT2;2 and PpNRT2;4 mRNAs as major NRT2 mRNA species. Promoter-LUC fusions constructed using PpNRT2;1 and PpNRT2;3 promoters also showed nitrogen-responsive differential expression of the reporter gene, indicating that the differential accumulation of PpNRT2;1 and PpNRT2;3 transcripts is ascribed primarily to regulation of transcription. PpNRT2;1 and PpNRT2;3 promoters of 1169 bp and 1124 bp in length, respectively, showed their specific response to nitrogen. However, the PpNRT2;3 promoter truncated to 633 bp showed only poor response to nitrate. This indicated that the -1243 to -634 region of PpNRT2;3 contains necessary elements for nitrate-responsive expression.
