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Alignment between PIN1 polarity and microtubule orientation in the shoot apical meristem reveals a tight coupling between morphogenesis and auxin transport.

Heisler MG, Hamant O, Krupinski P, Uyttewaal M, Ohno C, Jönsson H, Traas J, Meyerowitz EM - PLoS Biol. (2010)

Bottom Line: How this is achieved remains unclear.Our experiments reveal that both PIN1 localization and microtubule array orientation are likely to respond to a shared upstream regulator that appears to be biomechanical in nature.Lastly, through mathematical modeling we show that such a biophysical coupling could mediate the feedback loop between auxin and its transport that underlies plant phyllotaxis.

View Article: PubMed Central - PubMed

Affiliation: Division of Biology, California Institute of Technology, Pasadena, California, United States of America.

ABSTRACT
Morphogenesis during multicellular development is regulated by intercellular signaling molecules as well as by the mechanical properties of individual cells. In particular, normal patterns of organogenesis in plants require coordination between growth direction and growth magnitude. How this is achieved remains unclear. Here we show that in Arabidopsis thaliana, auxin patterning and cellular growth are linked through a correlated pattern of auxin efflux carrier localization and cortical microtubule orientation. Our experiments reveal that both PIN1 localization and microtubule array orientation are likely to respond to a shared upstream regulator that appears to be biomechanical in nature. Lastly, through mathematical modeling we show that such a biophysical coupling could mediate the feedback loop between auxin and its transport that underlies plant phyllotaxis.

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PIN1 and microtubules realign in response to laser ablation when auxin transport and distribution is altered.(A) Confocal projection showing the orientation of microtubule arrays at the pin1 mutant meristem summit after laser ablation. (B) Close-up of cells in (A), showing circumferential microtubule orientation in cells surrounding ablation site. Cells at least one cell distant from the wound exhibit circumferential orientation. Both microtubules (C) and PIN1 (D) reorient circumferentially around wounds 24 h after NPA treatment. Note that in (D) PIN1 is oriented away from the wound in cells several cells distant from the wound. Similar behavior is observed for microtubules (E) and PIN1 (F) after 2,4-D treatment. Dead cells are marked by propidium iodide staining (red). Note that two cells separated by an intervening cell are ablated in E. Scale bar for (A): 10 µm. Scale bars for (B–F): 5 µm.
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pbio-1000516-g004: PIN1 and microtubules realign in response to laser ablation when auxin transport and distribution is altered.(A) Confocal projection showing the orientation of microtubule arrays at the pin1 mutant meristem summit after laser ablation. (B) Close-up of cells in (A), showing circumferential microtubule orientation in cells surrounding ablation site. Cells at least one cell distant from the wound exhibit circumferential orientation. Both microtubules (C) and PIN1 (D) reorient circumferentially around wounds 24 h after NPA treatment. Note that in (D) PIN1 is oriented away from the wound in cells several cells distant from the wound. Similar behavior is observed for microtubules (E) and PIN1 (F) after 2,4-D treatment. Dead cells are marked by propidium iodide staining (red). Note that two cells separated by an intervening cell are ablated in E. Scale bar for (A): 10 µm. Scale bars for (B–F): 5 µm.

Mentions: First we conducted ablation experiments in the pin1 mutant background and observed the microtubule response. Untreated pin1 meristems exhibited microtubule orientations similar to wild-type, with a circumferential pattern around the lower meristem flanks and a more random pattern at the tip (data not shown). Likewise, we found that microtubules responded to ablation as they do in wild-type by becoming circumferentially oriented around the ablation site (Figure 4A and 4B). Next we treated apices with N-1-naphthylphthalamic acid (NPA), an auxin transport inhibitor, and examined both the PIN1 and microtubule response to ablation. Again, we found that in both cases the ablation response was the same as for wild-type untreated meristems (Figure 4C and 4D). Even several cell diameters from the ablated cell, PIN1 became oriented away from the ablation site, demonstrating that auxin transport is not required for this ablation-induced orientation signal (Figure 4D). Despite disruptions to auxin transport, differences in auxin concentration between cells may still conceivably be playing an instructive role during these experiments. To try to disrupt any such gradients we next applied 2,4-dichlorophenoxyacetic acid (2,4-D) to the meristem, an auxin analog that freely diffuses between cells, for 24 h before ablating and observing the PIN1 and microtubule response. Uniform PIN1 expression was observed after 24 h, demonstrating that 2,4-D effectively penetrated the tissue [5]. Nevertheless, as for untreated meristems, both PIN1 and the microtubule arrays of cells surrounding the ablated cell reoriented to point away from or form concentric patterns around the wound, respectively (Figure 4E and 4F). Again, at least in the case of PIN1, orientation away from the ablation site was observed at a distance (Figure 4F).


Alignment between PIN1 polarity and microtubule orientation in the shoot apical meristem reveals a tight coupling between morphogenesis and auxin transport.

Heisler MG, Hamant O, Krupinski P, Uyttewaal M, Ohno C, Jönsson H, Traas J, Meyerowitz EM - PLoS Biol. (2010)

PIN1 and microtubules realign in response to laser ablation when auxin transport and distribution is altered.(A) Confocal projection showing the orientation of microtubule arrays at the pin1 mutant meristem summit after laser ablation. (B) Close-up of cells in (A), showing circumferential microtubule orientation in cells surrounding ablation site. Cells at least one cell distant from the wound exhibit circumferential orientation. Both microtubules (C) and PIN1 (D) reorient circumferentially around wounds 24 h after NPA treatment. Note that in (D) PIN1 is oriented away from the wound in cells several cells distant from the wound. Similar behavior is observed for microtubules (E) and PIN1 (F) after 2,4-D treatment. Dead cells are marked by propidium iodide staining (red). Note that two cells separated by an intervening cell are ablated in E. Scale bar for (A): 10 µm. Scale bars for (B–F): 5 µm.
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Related In: Results  -  Collection

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pbio-1000516-g004: PIN1 and microtubules realign in response to laser ablation when auxin transport and distribution is altered.(A) Confocal projection showing the orientation of microtubule arrays at the pin1 mutant meristem summit after laser ablation. (B) Close-up of cells in (A), showing circumferential microtubule orientation in cells surrounding ablation site. Cells at least one cell distant from the wound exhibit circumferential orientation. Both microtubules (C) and PIN1 (D) reorient circumferentially around wounds 24 h after NPA treatment. Note that in (D) PIN1 is oriented away from the wound in cells several cells distant from the wound. Similar behavior is observed for microtubules (E) and PIN1 (F) after 2,4-D treatment. Dead cells are marked by propidium iodide staining (red). Note that two cells separated by an intervening cell are ablated in E. Scale bar for (A): 10 µm. Scale bars for (B–F): 5 µm.
Mentions: First we conducted ablation experiments in the pin1 mutant background and observed the microtubule response. Untreated pin1 meristems exhibited microtubule orientations similar to wild-type, with a circumferential pattern around the lower meristem flanks and a more random pattern at the tip (data not shown). Likewise, we found that microtubules responded to ablation as they do in wild-type by becoming circumferentially oriented around the ablation site (Figure 4A and 4B). Next we treated apices with N-1-naphthylphthalamic acid (NPA), an auxin transport inhibitor, and examined both the PIN1 and microtubule response to ablation. Again, we found that in both cases the ablation response was the same as for wild-type untreated meristems (Figure 4C and 4D). Even several cell diameters from the ablated cell, PIN1 became oriented away from the ablation site, demonstrating that auxin transport is not required for this ablation-induced orientation signal (Figure 4D). Despite disruptions to auxin transport, differences in auxin concentration between cells may still conceivably be playing an instructive role during these experiments. To try to disrupt any such gradients we next applied 2,4-dichlorophenoxyacetic acid (2,4-D) to the meristem, an auxin analog that freely diffuses between cells, for 24 h before ablating and observing the PIN1 and microtubule response. Uniform PIN1 expression was observed after 24 h, demonstrating that 2,4-D effectively penetrated the tissue [5]. Nevertheless, as for untreated meristems, both PIN1 and the microtubule arrays of cells surrounding the ablated cell reoriented to point away from or form concentric patterns around the wound, respectively (Figure 4E and 4F). Again, at least in the case of PIN1, orientation away from the ablation site was observed at a distance (Figure 4F).

Bottom Line: How this is achieved remains unclear.Our experiments reveal that both PIN1 localization and microtubule array orientation are likely to respond to a shared upstream regulator that appears to be biomechanical in nature.Lastly, through mathematical modeling we show that such a biophysical coupling could mediate the feedback loop between auxin and its transport that underlies plant phyllotaxis.

View Article: PubMed Central - PubMed

Affiliation: Division of Biology, California Institute of Technology, Pasadena, California, United States of America.

ABSTRACT
Morphogenesis during multicellular development is regulated by intercellular signaling molecules as well as by the mechanical properties of individual cells. In particular, normal patterns of organogenesis in plants require coordination between growth direction and growth magnitude. How this is achieved remains unclear. Here we show that in Arabidopsis thaliana, auxin patterning and cellular growth are linked through a correlated pattern of auxin efflux carrier localization and cortical microtubule orientation. Our experiments reveal that both PIN1 localization and microtubule array orientation are likely to respond to a shared upstream regulator that appears to be biomechanical in nature. Lastly, through mathematical modeling we show that such a biophysical coupling could mediate the feedback loop between auxin and its transport that underlies plant phyllotaxis.

Show MeSH