Limits...
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.

Show MeSH

Related in: MedlinePlus

Distribution of GUS activity under the control of the 5′ upstream region of the OsIPT4 (A, E and I), OsIPT5 (B, F and J), OsIPT7 (C, G and K) and OsIPT8 (D, H and L) genes. (A–D) Whole transformant seedlings. Close-ups of the root apex are shown in the insets at the bottom. (E–L) Cross-sections of vascular bundles in mature leaf blades (E–H) and seedling roots (I–L). ph, phloem; xp, xylem parenchyma. Scale bars, 1 cm (A–D) and 50 µm (E–L).
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3814184&req=5

pct127-F4: Distribution of GUS activity under the control of the 5′ upstream region of the OsIPT4 (A, E and I), OsIPT5 (B, F and J), OsIPT7 (C, G and K) and OsIPT8 (D, H and L) genes. (A–D) Whole transformant seedlings. Close-ups of the root apex are shown in the insets at the bottom. (E–L) Cross-sections of vascular bundles in mature leaf blades (E–H) and seedling roots (I–L). ph, phloem; xp, xylem parenchyma. Scale bars, 1 cm (A–D) and 50 µm (E–L).

Mentions: To reveal the tissue specificities of the nitrogen-dependent cytokinin biosynthesis genes, DNA fragments containing about 3 kb of the upstream sequences including the N-terminal regions of OsIPT4, OsIPT5, OsIPT7 and OsIPT8 were fused with the β-glucuronidase (GUS) coding sequence, and the constructs (designated OsIPT4pro:GUS, OsIPT5pro:GUS, OsIPT7pro:GUS and OsIPT8pro:GUS) were transformed into rice. We detected similar GUS staining patterns with 10–13 independent T1 transgenic lines of each construct, and T3 representative lines were further analyzed in detail (Fig. 4). In these transgenic lines, GUS activity was detected in roots, and less so in shoots (Fig. 4A–D). This finding was consistent with the results in Fig. 3. In roots, GUS staining patterns were essentially the same for all IPT promoters: staining was observed in vascular bundles of seminal and crown roots (Fig. 4I–L) but not in the apical meristems (Fig. 4A–D, insets). The staining patterns in the transformants did not change with different nitrogen sources (data not shown).Fig. 4


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)

Distribution of GUS activity under the control of the 5′ upstream region of the OsIPT4 (A, E and I), OsIPT5 (B, F and J), OsIPT7 (C, G and K) and OsIPT8 (D, H and L) genes. (A–D) Whole transformant seedlings. Close-ups of the root apex are shown in the insets at the bottom. (E–L) Cross-sections of vascular bundles in mature leaf blades (E–H) and seedling roots (I–L). ph, phloem; xp, xylem parenchyma. Scale bars, 1 cm (A–D) and 50 µm (E–L).
© Copyright Policy - creative-commons
Related In: Results  -  Collection

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

pct127-F4: Distribution of GUS activity under the control of the 5′ upstream region of the OsIPT4 (A, E and I), OsIPT5 (B, F and J), OsIPT7 (C, G and K) and OsIPT8 (D, H and L) genes. (A–D) Whole transformant seedlings. Close-ups of the root apex are shown in the insets at the bottom. (E–L) Cross-sections of vascular bundles in mature leaf blades (E–H) and seedling roots (I–L). ph, phloem; xp, xylem parenchyma. Scale bars, 1 cm (A–D) and 50 µm (E–L).
Mentions: To reveal the tissue specificities of the nitrogen-dependent cytokinin biosynthesis genes, DNA fragments containing about 3 kb of the upstream sequences including the N-terminal regions of OsIPT4, OsIPT5, OsIPT7 and OsIPT8 were fused with the β-glucuronidase (GUS) coding sequence, and the constructs (designated OsIPT4pro:GUS, OsIPT5pro:GUS, OsIPT7pro:GUS and OsIPT8pro:GUS) were transformed into rice. We detected similar GUS staining patterns with 10–13 independent T1 transgenic lines of each construct, and T3 representative lines were further analyzed in detail (Fig. 4). In these transgenic lines, GUS activity was detected in roots, and less so in shoots (Fig. 4A–D). This finding was consistent with the results in Fig. 3. In roots, GUS staining patterns were essentially the same for all IPT promoters: staining was observed in vascular bundles of seminal and crown roots (Fig. 4I–L) but not in the apical meristems (Fig. 4A–D, insets). The staining patterns in the transformants did not change with different nitrogen sources (data not shown).Fig. 4

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