title: Lack of Cytosolic Glutamine Synthetase1;2 Activity Reduces Nitrogen-Dependent Biosynthesis of Cytokinin Required for Axillary Bud Outgrowth in Rice Seedlings.
abstract: A mutation abolishing cytosolic glutamine synthetase1;2 (GS1;2) activity impairs assimilation of ammonium into glutamine in both roots and basal portions of shoots, and severely decreases axillary bud outgrowth (tillering) in mutant rice seedlings. Although the gs1;2 mutant phenotype is independent of strigolactone, which inhibits tillering, it also demonstrates glutamine- or related metabolite-responsive biosynthesis of cytokinin (CK), which promotes tillering. Here, we examined the connection between GS1;2 and CK biosynthesis during tillering, focusing on basal portions of the shoots as well as apical and axillary bud meristems in the gs1;2 mutant. Despite a sufficient ammonium supply, decreases in precursor CK contents and a decrease in ammonium assimilation into glutamine were observed in basal portions of mutant shoots. Reintroducing expression of OsGS1;2 cDNA driven by its own promoter restored precursor CK contents and ammonium assimilation to wild-type levels. In basal portions of the shoots, glutamine-responsive adenosine phosphate-isopentenyltransferase4 (OsIPT4), which is also predominant in rice roots, was the predominant isogene for IPT, which synthesizes CK. Cell-specific expression of OsIPT4 in phloem companion cells in nodal vascular anastomoses connected to the axillary bud vasculature also decreased in the gs1;2 mutant. Expression of CK-responsive type-A response regulator genes as local indicators of active CKs was also abolished in the axillary bud meristem of the mutant. These results suggest that the lack of GS1;2 activity decreased levels of glutamine or a related metabolite required for CK biosynthesis, causing a deficiency in active CK in the axillary bud meristem necessary for tillering.
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, Aoba, Sendai, Japan.
authors.forename: Miwa
authors.initials: M
authors.lastname: Ohashi
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, Aoba, Sendai, Japan.
authors.forename: Keiki
authors.initials: K
authors.lastname: Ishiyama
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, Aoba, Sendai, Japan.
authors.forename: Soichi
authors.initials: S
authors.lastname: Kojima
authors.affiliation: RIKEN Center for Sustainable Resource Science, Tsurumi, Yokohama, Japan.
authors.forename: Mikiko
authors.initials: M
authors.lastname: Kojima
authors.affiliation: RIKEN Center for Sustainable Resource Science, Tsurumi, Yokohama, Japan.|Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya, Japan.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Sakakibara
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, Aoba, Sendai, Japan.|University Research Administration Center, Tohoku University, Aoba, Sendai, Japan.|Division for Interdisciplinary Advanced Research and Education, Tohoku University, Aoba, Sendai, Japan.
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Yamaya
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, Aoba, Sendai, Japan.
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Hayakawa
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000235:genetics / Q000378:metabolism; D064751:Ammonium Compounds / Q000378:metabolism; D003583:Cytokinins / Q000378:metabolism*; D003600:Cytosol / Q000201:enzymology; D005974:Glutamate-Ammonia Ligase / Q000235:genetics / Q000378:metabolism*; D005973:Glutamine / Q000378:metabolism; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D009584:Nitrogen / Q000378:metabolism*; D012275:Oryza / Q000254:growth & development* / Q000378:metabolism*; D052585:Phloem / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018520:Plant Shoots / Q000254:growth & development / Q000378:metabolism; D036226:Seedlings / Q000235:genetics / Q000254:growth & development / Q000378:metabolism
chemical_list: D064751:Ammonium Compounds; D003583:Cytokinins; D007527:Isoenzymes; D010940:Plant Proteins; D005973:Glutamine; D019883:Alkyl and Aryl Transferases; C024274:adenylate isopentenyltransferase; D005974:Glutamate-Ammonia Ligase; D009584:Nitrogen
keywords: Axillary bud; Cytokinin; Cytosolic glutamine synthetase; Oryza sativa L; Tiller