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Nitrogen-dependent regulation of de novo cytokinin biosynthesis in rice: the role of glutamine metabolism as an additional signal.

Kamada-Nobusada T, Makita N, Kojima M, Sakakibara H - Plant Cell Physiol. (2013)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: RIKEN Center for Sustainable Resource Science, Tsurumi, Yokohama, 230-0045 Japan.

ABSTRACT
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.

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Accumulation of OsIPT transcripts in roots (left) and shoots (right) of rice seedlings hydroponically grown for 2 weeks in tap water. Total RNAs prepared from each organ were subjected to qPCR. The accumulations of transcripts are indicated as amounts per total RNA. qPCR was performed in triplicate, and mean values with the SD are shown.
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pct127-F3: Accumulation of OsIPT transcripts in roots (left) and shoots (right) of rice seedlings hydroponically grown for 2 weeks in tap water. Total RNAs prepared from each organ were subjected to qPCR. The accumulations of transcripts are indicated as amounts per total RNA. qPCR was performed in triplicate, and mean values with the SD are shown.

Mentions: When we analyzed the steady-state accumulation levels of OsIPT genes in rice seedlings before nitrogen application, we found OsIPT4, OsIPT7 and OsIPT8 transcripts abundantly accumulated in roots and shoots (Fig. 3). The OsIPT4 transcript accumulated mostly in roots, while the OsIPT8 transcript was most abundant in shoots. Accumulation levels of the OsIPT5 transcript were much lower than those of other nitrogen-responsive IPT genes. These results suggested that the expression of OsIPT4 on the one hand, and of OsIPT4, OsIPT7 and OsIPT8 on the other affected nitrogen-dependent cytokinin synthesis in roots and shoots, respectively.Fig. 3


Nitrogen-dependent regulation of de novo cytokinin biosynthesis in rice: the role of glutamine metabolism as an additional signal.

Kamada-Nobusada T, Makita N, Kojima M, Sakakibara H - Plant Cell Physiol. (2013)

Accumulation of OsIPT transcripts in roots (left) and shoots (right) of rice seedlings hydroponically grown for 2 weeks in tap water. Total RNAs prepared from each organ were subjected to qPCR. The accumulations of transcripts are indicated as amounts per total RNA. qPCR was performed in triplicate, and mean values with the SD are shown.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3814184&req=5

pct127-F3: Accumulation of OsIPT transcripts in roots (left) and shoots (right) of rice seedlings hydroponically grown for 2 weeks in tap water. Total RNAs prepared from each organ were subjected to qPCR. The accumulations of transcripts are indicated as amounts per total RNA. qPCR was performed in triplicate, and mean values with the SD are shown.
Mentions: When we analyzed the steady-state accumulation levels of OsIPT genes in rice seedlings before nitrogen application, we found OsIPT4, OsIPT7 and OsIPT8 transcripts abundantly accumulated in roots and shoots (Fig. 3). The OsIPT4 transcript accumulated mostly in roots, while the OsIPT8 transcript was most abundant in shoots. Accumulation levels of the OsIPT5 transcript were much lower than those of other nitrogen-responsive IPT genes. These results suggested that the expression of OsIPT4 on the one hand, and of OsIPT4, OsIPT7 and OsIPT8 on the other affected nitrogen-dependent cytokinin synthesis in roots and shoots, respectively.Fig. 3

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: RIKEN Center for Sustainable Resource Science, Tsurumi, Yokohama, 230-0045 Japan.

ABSTRACT
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.

Show MeSH
Related in: MedlinePlus