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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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Seedling root phenotype of AtRaptor1B-/- (B-) mutants. (A), (B). Col and B- seedlings on growth medium, four days after germination. The B- root has not penetrated the medium and is thick, hairy and coiled. (C) Col, A- and B- seedlings at 8 days after germination in light. Scale bar is in mm. (D) Same genotypes and age as C, grown in the dark. (E) Measurements of populations grown as in C, D. Root length is indicated in tan; shoot length is dark green. (F) B- and Col seedlings grown on vertical plates for 12 days, and then returned to horizontal growth for three days. B- roots are thin, straight and hairless on vertical plates (compare to 3B), and revert to coiled growth only in tissue generated after being placed horizontally. (G) Quantification of results in (F). B- seedlings grown on vertical plates are intermediate in length between flat-grown B- seedlings and Col seedlings. (H), (I) Col and B- root tips, viewed under bright field microscopy. Scale bar = 100 μm. B- root tips contain all the cell types seen in Col root tips, but the overall morphology is blunt and rounded compared to Col.
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Figure 3: Seedling root phenotype of AtRaptor1B-/- (B-) mutants. (A), (B). Col and B- seedlings on growth medium, four days after germination. The B- root has not penetrated the medium and is thick, hairy and coiled. (C) Col, A- and B- seedlings at 8 days after germination in light. Scale bar is in mm. (D) Same genotypes and age as C, grown in the dark. (E) Measurements of populations grown as in C, D. Root length is indicated in tan; shoot length is dark green. (F) B- and Col seedlings grown on vertical plates for 12 days, and then returned to horizontal growth for three days. B- roots are thin, straight and hairless on vertical plates (compare to 3B), and revert to coiled growth only in tissue generated after being placed horizontally. (G) Quantification of results in (F). B- seedlings grown on vertical plates are intermediate in length between flat-grown B- seedlings and Col seedlings. (H), (I) Col and B- root tips, viewed under bright field microscopy. Scale bar = 100 μm. B- root tips contain all the cell types seen in Col root tips, but the overall morphology is blunt and rounded compared to Col.

Mentions: As a first step toward characterizing these mutant lines, Col, 1A-/- and 1B-/- seedlings were germinated on culture medium. Col and 1A-/- seedlings were phenotypically indistinguishable. However, B-/- seedlings showed distinct root growth defects: roots were thick, coiled and densely covered with hairs, and the roots had difficulty penetrating the medium (Fig. 3A). Plate-grown 1B -/- seedlings were repeatedly shorter than Col or 1A-/- seedlings. Although dark grown 1B-/- seedlings were also shorter than Col or 1A-/-, the difference in size was much less (Fig. 3B). While dark-grown etiolated seedlings grow primarily through the expansion and division of embryonic hypocotyl cells, light-grown seedlings grow primarily through the production of cells from the root apical meristem. Thus the difference in size between Col, 1A-/- and 1B-/- seedlings results primarily from a reduction in root apical meristem growth rather than a general defect in cell expansion or metabolism.


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

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

Seedling root phenotype of AtRaptor1B-/- (B-) mutants. (A), (B). Col and B- seedlings on growth medium, four days after germination. The B- root has not penetrated the medium and is thick, hairy and coiled. (C) Col, A- and B- seedlings at 8 days after germination in light. Scale bar is in mm. (D) Same genotypes and age as C, grown in the dark. (E) Measurements of populations grown as in C, D. Root length is indicated in tan; shoot length is dark green. (F) B- and Col seedlings grown on vertical plates for 12 days, and then returned to horizontal growth for three days. B- roots are thin, straight and hairless on vertical plates (compare to 3B), and revert to coiled growth only in tissue generated after being placed horizontally. (G) Quantification of results in (F). B- seedlings grown on vertical plates are intermediate in length between flat-grown B- seedlings and Col seedlings. (H), (I) Col and B- root tips, viewed under bright field microscopy. Scale bar = 100 μm. B- root tips contain all the cell types seen in Col root tips, but the overall morphology is blunt and rounded compared to Col.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC1131892&req=5

Figure 3: Seedling root phenotype of AtRaptor1B-/- (B-) mutants. (A), (B). Col and B- seedlings on growth medium, four days after germination. The B- root has not penetrated the medium and is thick, hairy and coiled. (C) Col, A- and B- seedlings at 8 days after germination in light. Scale bar is in mm. (D) Same genotypes and age as C, grown in the dark. (E) Measurements of populations grown as in C, D. Root length is indicated in tan; shoot length is dark green. (F) B- and Col seedlings grown on vertical plates for 12 days, and then returned to horizontal growth for three days. B- roots are thin, straight and hairless on vertical plates (compare to 3B), and revert to coiled growth only in tissue generated after being placed horizontally. (G) Quantification of results in (F). B- seedlings grown on vertical plates are intermediate in length between flat-grown B- seedlings and Col seedlings. (H), (I) Col and B- root tips, viewed under bright field microscopy. Scale bar = 100 μm. B- root tips contain all the cell types seen in Col root tips, but the overall morphology is blunt and rounded compared to Col.
Mentions: As a first step toward characterizing these mutant lines, Col, 1A-/- and 1B-/- seedlings were germinated on culture medium. Col and 1A-/- seedlings were phenotypically indistinguishable. However, B-/- seedlings showed distinct root growth defects: roots were thick, coiled and densely covered with hairs, and the roots had difficulty penetrating the medium (Fig. 3A). Plate-grown 1B -/- seedlings were repeatedly shorter than Col or 1A-/- seedlings. Although dark grown 1B-/- seedlings were also shorter than Col or 1A-/-, the difference in size was much less (Fig. 3B). While dark-grown etiolated seedlings grow primarily through the expansion and division of embryonic hypocotyl cells, light-grown seedlings grow primarily through the production of cells from the root apical meristem. Thus the difference in size between Col, 1A-/- and 1B-/- seedlings results primarily from a reduction in root apical meristem growth rather than a general defect in cell expansion or metabolism.

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