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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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Microtubule and PIN1 orientations are correlated.(A) Immunolocalization of PIN1 (red) and α-tubulin (green) in a thick section through the surface of the meristem. Scale bar: 10 µm. (B) Close-up of the double PIN1–microtubule immunosignal in the boundary domain: PIN1 (red) and microtubule (green) patterns are correlated. Scale bar: 5 µm. (C) Examples of different degrees of correlation between microtubule bundle orientation and PIN1 localization, as quantified in (D). (D) Quantifications of the different classes of behavior in the center zone (CZ) and peripheral zone (PZ) of the meristem (n = 614 cells). (E–J) Correlations between PIN1 polarities and microtubule orientations similar to those seen in (B) are observed in living plants expressing PIN1-GFP (red) and TagRFP-MAP4 (green) in the boundary domain (E–H) and in incipient primordia (asterisk) (I and J). Scale bars for (E), (G), and (I): 5 µm.
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pbio-1000516-g001: Microtubule and PIN1 orientations are correlated.(A) Immunolocalization of PIN1 (red) and α-tubulin (green) in a thick section through the surface of the meristem. Scale bar: 10 µm. (B) Close-up of the double PIN1–microtubule immunosignal in the boundary domain: PIN1 (red) and microtubule (green) patterns are correlated. Scale bar: 5 µm. (C) Examples of different degrees of correlation between microtubule bundle orientation and PIN1 localization, as quantified in (D). (D) Quantifications of the different classes of behavior in the center zone (CZ) and peripheral zone (PZ) of the meristem (n = 614 cells). (E–J) Correlations between PIN1 polarities and microtubule orientations similar to those seen in (B) are observed in living plants expressing PIN1-GFP (red) and TagRFP-MAP4 (green) in the boundary domain (E–H) and in incipient primordia (asterisk) (I and J). Scale bars for (E), (G), and (I): 5 µm.

Mentions: We used dual immunolabeling to examine the spatial relationship between epidermal microtubule arrays and PIN1 localization. Although the degree of microtubule array anisotropy varies from cell to cell, in general we observed a good correlation between PIN1 localization and microtubule orientation, with PIN1 usually being localized towards an anticlinal wall that was parallel to the microtubules, as viewed from above. This was least obvious in the central meristem region (where microtubule orientation is known to be unstable [11]) (Figure 1A) and most obvious in the boundary regions between primordia and the meristem (Figure 1B). To analyze this in more detail we quantified the percentage of cells showing a clear correlation by measuring the angle formed between the orientation of PIN1 and the microtubule bundles (Figure 1C and 1D). For the central meristem region there was a clear correlation in the majority of those cells where assessment could be done (69%, Figure 1D). In the peripheral zone (which includes boundary regions) a greater proportion of cells showed a clear correlation (81%, Figure 1D), and this proportion rose to 100% when considering the boundary zone alone. Further correlations could also be detected when individual microtubule arrays exhibited more than one orientation, but these cases were considered not aligned overall in our classification scheme (Figure 1C and 1D). We also imaged living meristems expressing TagRFP-MAP4 and PIN1-GFP to help obtain a clear view of the correlation across the curved surface of the epidermis. In agreement with the immunolocalization data we observed clear correlations between PIN1 polarities and microtubule array orientations in boundary regions (Figure 1E–1H). In addition, we were able to assess those regions where new PIN1 convergences were forming (the future sites of new primordia) and found that here, too, PIN1 and microtubule orientations were well correlated (Figure 1I and 1J).


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)

Microtubule and PIN1 orientations are correlated.(A) Immunolocalization of PIN1 (red) and α-tubulin (green) in a thick section through the surface of the meristem. Scale bar: 10 µm. (B) Close-up of the double PIN1–microtubule immunosignal in the boundary domain: PIN1 (red) and microtubule (green) patterns are correlated. Scale bar: 5 µm. (C) Examples of different degrees of correlation between microtubule bundle orientation and PIN1 localization, as quantified in (D). (D) Quantifications of the different classes of behavior in the center zone (CZ) and peripheral zone (PZ) of the meristem (n = 614 cells). (E–J) Correlations between PIN1 polarities and microtubule orientations similar to those seen in (B) are observed in living plants expressing PIN1-GFP (red) and TagRFP-MAP4 (green) in the boundary domain (E–H) and in incipient primordia (asterisk) (I and J). Scale bars for (E), (G), and (I): 5 µm.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2957402&req=5

pbio-1000516-g001: Microtubule and PIN1 orientations are correlated.(A) Immunolocalization of PIN1 (red) and α-tubulin (green) in a thick section through the surface of the meristem. Scale bar: 10 µm. (B) Close-up of the double PIN1–microtubule immunosignal in the boundary domain: PIN1 (red) and microtubule (green) patterns are correlated. Scale bar: 5 µm. (C) Examples of different degrees of correlation between microtubule bundle orientation and PIN1 localization, as quantified in (D). (D) Quantifications of the different classes of behavior in the center zone (CZ) and peripheral zone (PZ) of the meristem (n = 614 cells). (E–J) Correlations between PIN1 polarities and microtubule orientations similar to those seen in (B) are observed in living plants expressing PIN1-GFP (red) and TagRFP-MAP4 (green) in the boundary domain (E–H) and in incipient primordia (asterisk) (I and J). Scale bars for (E), (G), and (I): 5 µm.
Mentions: We used dual immunolabeling to examine the spatial relationship between epidermal microtubule arrays and PIN1 localization. Although the degree of microtubule array anisotropy varies from cell to cell, in general we observed a good correlation between PIN1 localization and microtubule orientation, with PIN1 usually being localized towards an anticlinal wall that was parallel to the microtubules, as viewed from above. This was least obvious in the central meristem region (where microtubule orientation is known to be unstable [11]) (Figure 1A) and most obvious in the boundary regions between primordia and the meristem (Figure 1B). To analyze this in more detail we quantified the percentage of cells showing a clear correlation by measuring the angle formed between the orientation of PIN1 and the microtubule bundles (Figure 1C and 1D). For the central meristem region there was a clear correlation in the majority of those cells where assessment could be done (69%, Figure 1D). In the peripheral zone (which includes boundary regions) a greater proportion of cells showed a clear correlation (81%, Figure 1D), and this proportion rose to 100% when considering the boundary zone alone. Further correlations could also be detected when individual microtubule arrays exhibited more than one orientation, but these cases were considered not aligned overall in our classification scheme (Figure 1C and 1D). We also imaged living meristems expressing TagRFP-MAP4 and PIN1-GFP to help obtain a clear view of the correlation across the curved surface of the epidermis. In agreement with the immunolocalization data we observed clear correlations between PIN1 polarities and microtubule array orientations in boundary regions (Figure 1E–1H). In addition, we were able to assess those regions where new PIN1 convergences were forming (the future sites of new primordia) and found that here, too, PIN1 and microtubule orientations were well correlated (Figure 1I and 1J).

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