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The Arabidopsis AtRaptor genes are essential for post-embryonic plant growth.

Anderson GH, Veit B, Hanson MR - BMC Biol. (2005)

Bottom Line: AtRaptor transcripts accumulate in dividing and expanding cells and tissues.The data implicate the TOR signaling pathway, a major regulator of cell growth in yeast and metazoans, in the maintenance of growth from the shoot apical meristem in plants.These results provide insights into the ways in which TOR/Raptor signaling has been adapted to regulate plant growth and development, and indicate that in plants, as in other eukaryotes, there is some Raptor-independent TOR activity.

View Article: PubMed Central - HTML - PubMed

Affiliation: Molecular Biology and Genetics, Cornell University, Ithaca, 14853, USA. ganderson@salk.edu

ABSTRACT

Background: Flowering plant development is wholly reliant on growth from meristems, which contain totipotent cells that give rise to all post-embryonic organs in the plant. Plants are uniquely able to alter their development throughout their lifespan through the generation of new organs in response to external signals. To identify genes that regulate meristem-based growth, we considered homologues of Raptor proteins, which regulate cell growth in response to nutrients in yeast and metazoans as part of a signaling complex with the target of rapamycin (TOR) kinase.

Results: We identified AtRaptor1A and AtRaptor1B, two loci predicted to encode Raptor proteins in Arabidopsis. Disruption of AtRaptor1B yields plants with a wide range of developmental defects: roots are thick and grow slowly, leaf initiation and bolting are delayed and the shoot inflorescence shows reduced apical dominance. AtRaptor1A AtRaptor1B double mutants show normal embryonic development but are unable to maintain post-embryonic meristem-driven growth. AtRaptor transcripts accumulate in dividing and expanding cells and tissues.

Conclusion: The data implicate the TOR signaling pathway, a major regulator of cell growth in yeast and metazoans, in the maintenance of growth from the shoot apical meristem in plants. These results provide insights into the ways in which TOR/Raptor signaling has been adapted to regulate plant growth and development, and indicate that in plants, as in other eukaryotes, there is some Raptor-independent TOR activity.

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AtRaptor accumulation pattern. (A) AtRaptor transcripts accumulate throughout the floral shoot apex, stem and differentiating floral buds. Accumulation is not confined to dividing or meristematic cells, but fades in intensity away from the apex. (B) Adjacent tissue slice, probed with actin. AtRaptor and actin transcript accumulation patterns differ. (C) In silico analysis of AtRaptor1A (left) and AtRaptor1B (right) accumulation from 1434 developmental gene chip experiments. Results are given by developmental stage (X-axis) and in terms of gene chip-normalized expression levels (Y-axis). Expression levels are shown to scale. Developmental stages are as follows: 1, 1.0–5.9 days; 2, 6.0–13.9 days; 3, 14.0–17.9 days; 4, 18.0–20.9 days; 5, 21.0–24.9 days; 6, 25.0–28.9 days; 7, 29.0–35.9 days; 8, 36.0–44.9 days; 9, 45.0–50.0 days. Analyses performed via the genevestigator website .
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Figure 6: AtRaptor accumulation pattern. (A) AtRaptor transcripts accumulate throughout the floral shoot apex, stem and differentiating floral buds. Accumulation is not confined to dividing or meristematic cells, but fades in intensity away from the apex. (B) Adjacent tissue slice, probed with actin. AtRaptor and actin transcript accumulation patterns differ. (C) In silico analysis of AtRaptor1A (left) and AtRaptor1B (right) accumulation from 1434 developmental gene chip experiments. Results are given by developmental stage (X-axis) and in terms of gene chip-normalized expression levels (Y-axis). Expression levels are shown to scale. Developmental stages are as follows: 1, 1.0–5.9 days; 2, 6.0–13.9 days; 3, 14.0–17.9 days; 4, 18.0–20.9 days; 5, 21.0–24.9 days; 6, 25.0–28.9 days; 7, 29.0–35.9 days; 8, 36.0–44.9 days; 9, 45.0–50.0 days. Analyses performed via the genevestigator website .

Mentions: A combination of in situ RNA hybridization and in silico expression analysis was used to determine the RNA accumulation pattern of AtRaptor transcripts in Arabidopsis. The AtRaptor1B cDNA sequence was used to generate an AtRaptor probe to assay transcript accumulation in the shoot tips of wild-type plants. Since AtRaptor1A and AtRaptor1B show 80% identity through the length of their transcripts, this probe likely detected expression of both loci.AtRaptor transcripts were detected throughout the shoot tip, in all organs of the differentiating floral bud, and deep into the differentiated inflorescence stem (Fig. 6A). Signal intensity faded with the distance from the shoot apex. This accumulation pattern differed from that of actin (Fig. 6B), which was more prominent in dividing cells of the apex. Notably, AtRaptor accumulation is not restricted to the primary shoot apex.


The Arabidopsis AtRaptor genes are essential for post-embryonic plant growth.

Anderson GH, Veit B, Hanson MR - BMC Biol. (2005)

AtRaptor accumulation pattern. (A) AtRaptor transcripts accumulate throughout the floral shoot apex, stem and differentiating floral buds. Accumulation is not confined to dividing or meristematic cells, but fades in intensity away from the apex. (B) Adjacent tissue slice, probed with actin. AtRaptor and actin transcript accumulation patterns differ. (C) In silico analysis of AtRaptor1A (left) and AtRaptor1B (right) accumulation from 1434 developmental gene chip experiments. Results are given by developmental stage (X-axis) and in terms of gene chip-normalized expression levels (Y-axis). Expression levels are shown to scale. Developmental stages are as follows: 1, 1.0–5.9 days; 2, 6.0–13.9 days; 3, 14.0–17.9 days; 4, 18.0–20.9 days; 5, 21.0–24.9 days; 6, 25.0–28.9 days; 7, 29.0–35.9 days; 8, 36.0–44.9 days; 9, 45.0–50.0 days. Analyses performed via the genevestigator website .
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Related In: Results  -  Collection

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Figure 6: AtRaptor accumulation pattern. (A) AtRaptor transcripts accumulate throughout the floral shoot apex, stem and differentiating floral buds. Accumulation is not confined to dividing or meristematic cells, but fades in intensity away from the apex. (B) Adjacent tissue slice, probed with actin. AtRaptor and actin transcript accumulation patterns differ. (C) In silico analysis of AtRaptor1A (left) and AtRaptor1B (right) accumulation from 1434 developmental gene chip experiments. Results are given by developmental stage (X-axis) and in terms of gene chip-normalized expression levels (Y-axis). Expression levels are shown to scale. Developmental stages are as follows: 1, 1.0–5.9 days; 2, 6.0–13.9 days; 3, 14.0–17.9 days; 4, 18.0–20.9 days; 5, 21.0–24.9 days; 6, 25.0–28.9 days; 7, 29.0–35.9 days; 8, 36.0–44.9 days; 9, 45.0–50.0 days. Analyses performed via the genevestigator website .
Mentions: A combination of in situ RNA hybridization and in silico expression analysis was used to determine the RNA accumulation pattern of AtRaptor transcripts in Arabidopsis. The AtRaptor1B cDNA sequence was used to generate an AtRaptor probe to assay transcript accumulation in the shoot tips of wild-type plants. Since AtRaptor1A and AtRaptor1B show 80% identity through the length of their transcripts, this probe likely detected expression of both loci.AtRaptor transcripts were detected throughout the shoot tip, in all organs of the differentiating floral bud, and deep into the differentiated inflorescence stem (Fig. 6A). Signal intensity faded with the distance from the shoot apex. This accumulation pattern differed from that of actin (Fig. 6B), which was more prominent in dividing cells of the apex. Notably, AtRaptor accumulation is not restricted to the primary shoot apex.

Bottom Line: AtRaptor transcripts accumulate in dividing and expanding cells and tissues.The data implicate the TOR signaling pathway, a major regulator of cell growth in yeast and metazoans, in the maintenance of growth from the shoot apical meristem in plants.These results provide insights into the ways in which TOR/Raptor signaling has been adapted to regulate plant growth and development, and indicate that in plants, as in other eukaryotes, there is some Raptor-independent TOR activity.

View Article: PubMed Central - HTML - PubMed

Affiliation: Molecular Biology and Genetics, Cornell University, Ithaca, 14853, USA. ganderson@salk.edu

ABSTRACT

Background: Flowering plant development is wholly reliant on growth from meristems, which contain totipotent cells that give rise to all post-embryonic organs in the plant. Plants are uniquely able to alter their development throughout their lifespan through the generation of new organs in response to external signals. To identify genes that regulate meristem-based growth, we considered homologues of Raptor proteins, which regulate cell growth in response to nutrients in yeast and metazoans as part of a signaling complex with the target of rapamycin (TOR) kinase.

Results: We identified AtRaptor1A and AtRaptor1B, two loci predicted to encode Raptor proteins in Arabidopsis. Disruption of AtRaptor1B yields plants with a wide range of developmental defects: roots are thick and grow slowly, leaf initiation and bolting are delayed and the shoot inflorescence shows reduced apical dominance. AtRaptor1A AtRaptor1B double mutants show normal embryonic development but are unable to maintain post-embryonic meristem-driven growth. AtRaptor transcripts accumulate in dividing and expanding cells and tissues.

Conclusion: The data implicate the TOR signaling pathway, a major regulator of cell growth in yeast and metazoans, in the maintenance of growth from the shoot apical meristem in plants. These results provide insights into the ways in which TOR/Raptor signaling has been adapted to regulate plant growth and development, and indicate that in plants, as in other eukaryotes, there is some Raptor-independent TOR activity.

Show MeSH
Related in: MedlinePlus