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Mathematical modelling of WOX5- and CLE40-mediated columella stem cell homeostasis in Arabidopsis.

Richards S, Wink RH, Simon R - J. Exp. Bot. (2015)

Bottom Line: We have also found that WOX5 contributes to, but is not absolutely necessary for, CSC maintenance.Furthermore, our modelling led us to postulate an additional signalling molecule that promotes CSC maintenance.We propose that this WOX5-independent signal originates in the QC, is targeted by CLE40 signalling and is capable of maintaining CSCs.

View Article: PubMed Central - PubMed

Affiliation: Institute of Developmental Genetics, Heinrich Heine University, 40225 Düsseldorf, Germany.

No MeSH data available.


Representation of C/W/X multi-cell model predictions of CSC fate and C/W/X localization. Gradients of W as predicted by the model are shown on the left sides of roots, while X gradients are shown on the right. Expected number of CSC rows, based on experimental results, is shown in parentheses, while those based on model predictions are shown next to the root diagram. The model outcomes can emulate the expected number of rows for wild type, wox5 mutants, cle40 mutants, wox5/cle40 double mutants, constitutively expressed WOX5 (iWOX5), and the addition of sufficient amounts of CLE40p (+CLE40p). We have also used the model to predict results of experiments that have not yet been completed to aid in later validations of this model. Tripling the W production rate (3× WOX5) is expected to yield more layers of stem cells. In the case of these parameter values, it is expected to result in two layers.
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Figure 9: Representation of C/W/X multi-cell model predictions of CSC fate and C/W/X localization. Gradients of W as predicted by the model are shown on the left sides of roots, while X gradients are shown on the right. Expected number of CSC rows, based on experimental results, is shown in parentheses, while those based on model predictions are shown next to the root diagram. The model outcomes can emulate the expected number of rows for wild type, wox5 mutants, cle40 mutants, wox5/cle40 double mutants, constitutively expressed WOX5 (iWOX5), and the addition of sufficient amounts of CLE40p (+CLE40p). We have also used the model to predict results of experiments that have not yet been completed to aid in later validations of this model. Tripling the W production rate (3× WOX5) is expected to yield more layers of stem cells. In the case of these parameter values, it is expected to result in two layers.

Mentions: We designed another model, the C/W/X multi-cell model, where X was included with the same role and relationships as W in the C/W multi-cell model (Fig. 8). This C/W/X multi-cell model is able to describe the most common outcomes of all of the experimental results to which we have access, including that of wox5-1/cle40-2 mutants (Fig. 9). We then used the C/W/X model to predict the phenotype of wox5/x mutants. Since the model assumes that either W or X is necessary to maintain CSC fate, those roots are expected to have no CSCs. The model predicts that the number of CSC layers would depend on the rate of WOX5 expression, so that increasing the rate of W production while still keeping W expression restricted to the QC would result in more stem cell layers due to a higher flux of W to distal cells. In the C/W/X multi-cell model, X functions redundantly with WOX5, perhaps protecting the pluripotent nature of the QC and keeping it from differentiating when WOX5 levels are low. The phenotypes of wox5-1 mutants suggest that X should be less abundant or less effective at CSC maintenance than the WOX5-dependent signal (W) in the presence of CLE40, since wox5-1 mutants have less CSCs than wox5-1/cle40-2 mutants. We simulated this in the model by making the production rate of X less than that of W. Despite the smaller direct effect of X on CSC fate, it had a significant impact on sensitivity of the model to changes in parameters controlling W (Table 2). Due to the buffering activity of X, the model was less sensitive to the production and diffusion rates of W. We conclude that the activity of X allows the network controlling CSC fate to be more robust to perturbations in the levels of WOX5. Starch granules can be found in the QC infrequently in wox5-1 mutants, but frequently when a substantial amount of synthetic CLE40p is added to wox5-1 mutants. The model would suggest that the CLE40p is negatively affecting X in this case.


Mathematical modelling of WOX5- and CLE40-mediated columella stem cell homeostasis in Arabidopsis.

Richards S, Wink RH, Simon R - J. Exp. Bot. (2015)

Representation of C/W/X multi-cell model predictions of CSC fate and C/W/X localization. Gradients of W as predicted by the model are shown on the left sides of roots, while X gradients are shown on the right. Expected number of CSC rows, based on experimental results, is shown in parentheses, while those based on model predictions are shown next to the root diagram. The model outcomes can emulate the expected number of rows for wild type, wox5 mutants, cle40 mutants, wox5/cle40 double mutants, constitutively expressed WOX5 (iWOX5), and the addition of sufficient amounts of CLE40p (+CLE40p). We have also used the model to predict results of experiments that have not yet been completed to aid in later validations of this model. Tripling the W production rate (3× WOX5) is expected to yield more layers of stem cells. In the case of these parameter values, it is expected to result in two layers.
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Related In: Results  -  Collection

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Figure 9: Representation of C/W/X multi-cell model predictions of CSC fate and C/W/X localization. Gradients of W as predicted by the model are shown on the left sides of roots, while X gradients are shown on the right. Expected number of CSC rows, based on experimental results, is shown in parentheses, while those based on model predictions are shown next to the root diagram. The model outcomes can emulate the expected number of rows for wild type, wox5 mutants, cle40 mutants, wox5/cle40 double mutants, constitutively expressed WOX5 (iWOX5), and the addition of sufficient amounts of CLE40p (+CLE40p). We have also used the model to predict results of experiments that have not yet been completed to aid in later validations of this model. Tripling the W production rate (3× WOX5) is expected to yield more layers of stem cells. In the case of these parameter values, it is expected to result in two layers.
Mentions: We designed another model, the C/W/X multi-cell model, where X was included with the same role and relationships as W in the C/W multi-cell model (Fig. 8). This C/W/X multi-cell model is able to describe the most common outcomes of all of the experimental results to which we have access, including that of wox5-1/cle40-2 mutants (Fig. 9). We then used the C/W/X model to predict the phenotype of wox5/x mutants. Since the model assumes that either W or X is necessary to maintain CSC fate, those roots are expected to have no CSCs. The model predicts that the number of CSC layers would depend on the rate of WOX5 expression, so that increasing the rate of W production while still keeping W expression restricted to the QC would result in more stem cell layers due to a higher flux of W to distal cells. In the C/W/X multi-cell model, X functions redundantly with WOX5, perhaps protecting the pluripotent nature of the QC and keeping it from differentiating when WOX5 levels are low. The phenotypes of wox5-1 mutants suggest that X should be less abundant or less effective at CSC maintenance than the WOX5-dependent signal (W) in the presence of CLE40, since wox5-1 mutants have less CSCs than wox5-1/cle40-2 mutants. We simulated this in the model by making the production rate of X less than that of W. Despite the smaller direct effect of X on CSC fate, it had a significant impact on sensitivity of the model to changes in parameters controlling W (Table 2). Due to the buffering activity of X, the model was less sensitive to the production and diffusion rates of W. We conclude that the activity of X allows the network controlling CSC fate to be more robust to perturbations in the levels of WOX5. Starch granules can be found in the QC infrequently in wox5-1 mutants, but frequently when a substantial amount of synthetic CLE40p is added to wox5-1 mutants. The model would suggest that the CLE40p is negatively affecting X in this case.

Bottom Line: We have also found that WOX5 contributes to, but is not absolutely necessary for, CSC maintenance.Furthermore, our modelling led us to postulate an additional signalling molecule that promotes CSC maintenance.We propose that this WOX5-independent signal originates in the QC, is targeted by CLE40 signalling and is capable of maintaining CSCs.

View Article: PubMed Central - PubMed

Affiliation: Institute of Developmental Genetics, Heinrich Heine University, 40225 Düsseldorf, Germany.

No MeSH data available.