Abstract
In higher plants, nitrate reductase (NR) is phosphorylated in the dark and then inactivated by binding of a 14-3-3 protein. The phosphotylation site for the 14-3-3 binding is conserved in the hinge-1 region of the plant NR proteins. Physcomitrella patens has two NR species, whose molybdenum cofactor binding domains, heme domains, and FAD domains are 60-70% identical (90-95% similar) with the corresponding domains of higher plant NRs. However, their hinge-1 regions showed only 30-40% identity (70-80% similarity) with those of the plant NRs and lacked the sequence signature conserved in the regulatory region. Also, Physcomitrella showed nitrate uptake after dark transition, indicating that transport and reduction of nitrate proceed in the dark. We hence concluded that Physcomitrella has no mechanism for posttranslational regulation of NR through phosphorylation and binding of the 14-3-3 protein.
