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

Effects of methionine sulfoximine (MSX) pre-treatment on the induction of OsIPT transcript accumulation by nitrogen compounds. Rice seedlings were hydroponically grown in tap water for 11 d after sowing and then on nitrogen-free culture medium for 3 d. The seedlings were pre-treated with 1 mM MSX for 2 h and then incubated with (A), 1 mM KCl, 1 mM NH4Cl or 50 mM of the indicated amino acids for 3 h; or (B), 10 mM KCl or 10 mM KNO3 for 3 h. In (B), samples without MSX pre-treatment were also prepared. Total RNA prepared from the roots was subjected to qPCR. The amounts of transcripts were normalized with respect to the value in the KCl treatment. qPCR was performed in triplicate, and mean values with the SD are shown.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

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

pct127-F6: Effects of methionine sulfoximine (MSX) pre-treatment on the induction of OsIPT transcript accumulation by nitrogen compounds. Rice seedlings were hydroponically grown in tap water for 11 d after sowing and then on nitrogen-free culture medium for 3 d. The seedlings were pre-treated with 1 mM MSX for 2 h and then incubated with (A), 1 mM KCl, 1 mM NH4Cl or 50 mM of the indicated amino acids for 3 h; or (B), 10 mM KCl or 10 mM KNO3 for 3 h. In (B), samples without MSX pre-treatment were also prepared. Total RNA prepared from the roots was subjected to qPCR. The amounts of transcripts were normalized with respect to the value in the KCl treatment. qPCR was performed in triplicate, and mean values with the SD are shown.

Mentions: To obtain information about the regulation of nitrogen-dependent OsIPT expression, we examined the effects of l-methionine sulfoximine (MSX), an inhibitor of GS (Pace and Mcdermott 1952). Roots of rice seedlings grown for 2 weeks without nitrogen were pre-treated with MSX before ammonium or amino acids were applied. Pre-treatment with MSX completely inhibited the ammonium-induced accumulation of OsIPT4 and OsIPT5 transcripts (Fig. 6A), indicating that ammonium itself is not a direct inducing signal. On the other hand, application of glutamine induced expression of OsIPT genes as well as that of NADH-GOGAT1, a glutamine-responsive gene (Hirose et al. 1997). Other amino acids had no comparable effects. Application of glutamine increased the cytokinin concentration in roots (Supplementary Fig. S3). These results suggested that glutamine or a related metabolite regulates the cytokinin concentration via nitrogen-dependent OsIPT4 and OsIPT5 expression.Fig. 6


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)

Effects of methionine sulfoximine (MSX) pre-treatment on the induction of OsIPT transcript accumulation by nitrogen compounds. Rice seedlings were hydroponically grown in tap water for 11 d after sowing and then on nitrogen-free culture medium for 3 d. The seedlings were pre-treated with 1 mM MSX for 2 h and then incubated with (A), 1 mM KCl, 1 mM NH4Cl or 50 mM of the indicated amino acids for 3 h; or (B), 10 mM KCl or 10 mM KNO3 for 3 h. In (B), samples without MSX pre-treatment were also prepared. Total RNA prepared from the roots was subjected to qPCR. The amounts of transcripts were normalized with respect to the value in the KCl treatment. 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-F6: Effects of methionine sulfoximine (MSX) pre-treatment on the induction of OsIPT transcript accumulation by nitrogen compounds. Rice seedlings were hydroponically grown in tap water for 11 d after sowing and then on nitrogen-free culture medium for 3 d. The seedlings were pre-treated with 1 mM MSX for 2 h and then incubated with (A), 1 mM KCl, 1 mM NH4Cl or 50 mM of the indicated amino acids for 3 h; or (B), 10 mM KCl or 10 mM KNO3 for 3 h. In (B), samples without MSX pre-treatment were also prepared. Total RNA prepared from the roots was subjected to qPCR. The amounts of transcripts were normalized with respect to the value in the KCl treatment. qPCR was performed in triplicate, and mean values with the SD are shown.
Mentions: To obtain information about the regulation of nitrogen-dependent OsIPT expression, we examined the effects of l-methionine sulfoximine (MSX), an inhibitor of GS (Pace and Mcdermott 1952). Roots of rice seedlings grown for 2 weeks without nitrogen were pre-treated with MSX before ammonium or amino acids were applied. Pre-treatment with MSX completely inhibited the ammonium-induced accumulation of OsIPT4 and OsIPT5 transcripts (Fig. 6A), indicating that ammonium itself is not a direct inducing signal. On the other hand, application of glutamine induced expression of OsIPT genes as well as that of NADH-GOGAT1, a glutamine-responsive gene (Hirose et al. 1997). Other amino acids had no comparable effects. Application of glutamine increased the cytokinin concentration in roots (Supplementary Fig. S3). These results suggested that glutamine or a related metabolite regulates the cytokinin concentration via nitrogen-dependent OsIPT4 and OsIPT5 expression.Fig. 6

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