Abstract
Nitrate transporter (NRT) mediates the first step of nitrate assimilation. We have already identified five NRT2 genes, encoding the main components of NRT in Physcomitrella patens. As NAR2 is required for nitrate transport by NRT2 in Chramydomonous, we further cloned three Nar2 genes from Physcomitrella. Expression of these genes was induced after transfer of the cells grown with ammonium to nitrate-containing medium or nitrite-containing medium. However, expression patterns in each medium were different. This result indicated that the nitrate assimilation genes are induced not only by nitrate but also by nitrite, and that the induction mechanism with nitrite is different from the nitrate induction system that has been characterized in other organisms. Finally, five NRT2s and three Nar2s were classified into two groups: the one strongly induced by nitrate or nitrite, and the other induced by nitrogen deprivation with only slight influence of nitrate and nitrite.
