Nitrogen-dependent regulation of de novo cytokinin biosynthesis in rice: the role of glutamine metabolism as an additional signal.
Cytokinin activity in plants is closely related to nitrogen availability, and an Arabidopsis gene for adenosine phosphate-isopentenyltransferase (IPT), IPT3, is regulated by inorganic nitrogen sources in a nitrate-specific manner. In this study, we have identified another regulatory system of cytokinin de novo biosynthesis in response to nitrogen status. In rice, OsIPT4, OsIPT5, OsIPT7 and OsIPT8 were up-regulated in response to exogenously applied nitrate and ammonium, with accompanying accumulation of cytokinins. Pre-treatment of roots with l-methionine sulfoximine, a potent inhibitor of glutamine synthetase, abolished the nitrate- and ammonium-dependent induction of OsIPT4 and OsIPT5, while glutamine application induced their expression. Thus, neither nitrate nor ammonium, but glutamine or a related metabolite, is essential for the induction of these IPT genes in rice. On the other hand, glutamine-dependent induction of IPT3 occurs in Arabidopsis, at least to some extent. In transgenic lines repressing the expression of OsIPT4, which is the dominant IPT in rice roots, the nitrogen-dependent increase of cytokinin in the xylem sap was significantly reduced, and seedling shoot growth was retarded despite sufficient nitrogen. We conclude that plants possess multiple regulation systems for nitrogen-dependent cytokinin biosynthesis to modulate growth in response to nitrogen availability.
RIKEN Center for Sustainable Resource Science, Tsurumi, Yokohama, 230-0045 Japan.
Tomoe
T
Kamada-Nobusada
Nobue
N
Makita
Mikiko
M
Kojima
Hitoshi
H
Sakakibara
D019883:Alkyl and Aryl Transferases / Q000235:genetics* / Q000378:metabolism; D064751:Ammonium Compounds / Q000378:metabolism; D017360:Arabidopsis / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D003583:Cytokinins / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D005973:Glutamine / Q000378:metabolism*; D008969:Molecular Sequence Data; D009566:Nitrates / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism; D012275:Oryza / Q000166:cytology / Q000235:genetics* / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D018520:Plant Shoots / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D058526:Plant Vascular Bundle / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D011993:Recombinant Fusion Proteins; D036226:Seedlings / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D017422:Sequence Analysis, DNA; D015398:Signal Transduction; D013045:Species Specificity
D064751:Ammonium Compounds; D003583:Cytokinins; D009566:Nitrates; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D005973:Glutamine; D019883:Alkyl and Aryl Transferases; C024274:adenylate isopentenyltransferase; D009584:Nitrogen
Ammonium; Arabidopsis thaliana; Cytokinin; Glutamine; Nitrate; Oryza sativa