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Over-expression of Arabidopsis AtCHR23 chromatin remodeling ATPase results in increased variability of growth and gene expression.

Folta A, Severing EI, Krauskopf J, van de Geest H, Verver J, Nap JP, Mlynarova L - BMC Plant Biol. (2014)

Bottom Line: Already modest (2-fold) over-expression of the AtCHR23 ATPase gene in Arabidopsis results in overall reduced growth compared to the wild-type.Detailed analyses show that in the root, the reduction of growth is due to reduced cell elongation.In contrast, the knockout mutation of AtCHR23 does not lead to such visible phenotypic effects.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratory of Molecular Biology, Plant Sciences Group, Wageningen University and Research Centre, Droevendaalsesteeg 1, Wageningen 6708 PB, The Netherlands. ludmila.mlynarova@wur.nl.

ABSTRACT

Background: Plants are sessile organisms that deal with their -sometimes adverse- environment in well-regulated ways. Chromatin remodeling involving SWI/SNF2-type ATPases is thought to be an important epigenetic mechanism for the regulation of gene expression in different developmental programs and for integrating these programs with the response to environmental signals. In this study, we report on the role of chromatin remodeling in Arabidopsis with respect to the variability of growth and gene expression in relationship to environmental conditions.

Results: Already modest (2-fold) over-expression of the AtCHR23 ATPase gene in Arabidopsis results in overall reduced growth compared to the wild-type. Detailed analyses show that in the root, the reduction of growth is due to reduced cell elongation. The reduced-growth phenotype requires sufficient light and is magnified by applying deliberate abiotic (salt, osmotic) stress. In contrast, the knockout mutation of AtCHR23 does not lead to such visible phenotypic effects. In addition, we show that over-expression of AtCHR23 increases the variability of growth in populations of genetically identical plants. These data indicate that accurate and controlled expression of AtCHR23 contributes to the stability or robustness of growth. Detailed RNAseq analyses demonstrate that upon AtCHR23 over-expression also the variation of gene expression is increased in a subset of genes that associate with environmental stress. The larger variation of gene expression is confirmed in individual plants with the help of independent qRT-PCR analysis.

Conclusions: Over-expression of AtCHR23 gives Arabidopsis a phenotype that is markedly different from the growth arrest phenotype observed upon over-expression of AtCHR12, the paralog of AtCHR23, in response to abiotic stress. This demonstrates functional sub-specialization of highly similar ATPases in Arabidopsis. Over-expression of AtCHR23 increases the variability of growth among genetically identical individuals in a way that is consistent with increased variability of expression of a distinct subset of genes that associate with environmental stress. We propose that ATCHR23-mediated chromatin remodeling is a potential component of a buffer system in plants that protects against environmentally-induced phenotypic and transcriptional variation.

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AtCHR23 over-expression affects cell elongation. (A) Confocal images of 6-day-old Col wild-type and AtCHR23-4ov mutant roots grown at 23°C in long day conditions stained with propidium iodide. Arrows indicate the quiescent center, arrowheads indicate the boundary between the proximal meristem and elongation zone of the root. Scale bar: 50 μm. (B) Number of cells (± SD) counted in meristem (left) and mean (± SD) meristem length (right) in Col wild-type and AtCHR23-4ov mutant. (C) Mean (± SD) length of fully elongated cells in elongation zone (left) and mean (± SD) length of the elongation zone (right) in Col wild-type and AtCHR23-4ov mutant. Asterisks indicate significant differences from the wild type: ***, P < 0.001.
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Figure 3: AtCHR23 over-expression affects cell elongation. (A) Confocal images of 6-day-old Col wild-type and AtCHR23-4ov mutant roots grown at 23°C in long day conditions stained with propidium iodide. Arrows indicate the quiescent center, arrowheads indicate the boundary between the proximal meristem and elongation zone of the root. Scale bar: 50 μm. (B) Number of cells (± SD) counted in meristem (left) and mean (± SD) meristem length (right) in Col wild-type and AtCHR23-4ov mutant. (C) Mean (± SD) length of fully elongated cells in elongation zone (left) and mean (± SD) length of the elongation zone (right) in Col wild-type and AtCHR23-4ov mutant. Asterisks indicate significant differences from the wild type: ***, P < 0.001.

Mentions: To determine whether the reduction of root length is due to reduced cell division or reduced cell elongation, we analyzed the size of the meristematic and elongation zone of 6-day-old seedlings. AtCHR23-4ov roots exhibited a normal cellular patterning compared to the wild-type (Figure 3A). For meristem we measured both the length of the meristematic zone and the number of meristematic cortex cells. None of them differ between wild-type and mutant roots (Figure 3B). To further assess the role of cell division, we also used the cell G2-M phase cycle marker pCYCB1;1:CYCB1;1-GUS [29]. No clear difference in the pattern (Additional file1: Figure S2) and number of GUS-positive cells was observed between the wild-type and the over-expressing mutant (data not shown). This is consistent with meristem size of wild-type and mutant (Figure 3B). On the other hand, the mutant showed a significantly shortened (16.8%) elongation zone relative to the wild-type as well as reduced length (23.1%) of the fully elongated cells (Figure 3C). Taken together, these results indicate that the major effect of AtCHR23 up-regulation in the root is the reduction of cell elongation.


Over-expression of Arabidopsis AtCHR23 chromatin remodeling ATPase results in increased variability of growth and gene expression.

Folta A, Severing EI, Krauskopf J, van de Geest H, Verver J, Nap JP, Mlynarova L - BMC Plant Biol. (2014)

AtCHR23 over-expression affects cell elongation. (A) Confocal images of 6-day-old Col wild-type and AtCHR23-4ov mutant roots grown at 23°C in long day conditions stained with propidium iodide. Arrows indicate the quiescent center, arrowheads indicate the boundary between the proximal meristem and elongation zone of the root. Scale bar: 50 μm. (B) Number of cells (± SD) counted in meristem (left) and mean (± SD) meristem length (right) in Col wild-type and AtCHR23-4ov mutant. (C) Mean (± SD) length of fully elongated cells in elongation zone (left) and mean (± SD) length of the elongation zone (right) in Col wild-type and AtCHR23-4ov mutant. Asterisks indicate significant differences from the wild type: ***, P < 0.001.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC3987066&req=5

Figure 3: AtCHR23 over-expression affects cell elongation. (A) Confocal images of 6-day-old Col wild-type and AtCHR23-4ov mutant roots grown at 23°C in long day conditions stained with propidium iodide. Arrows indicate the quiescent center, arrowheads indicate the boundary between the proximal meristem and elongation zone of the root. Scale bar: 50 μm. (B) Number of cells (± SD) counted in meristem (left) and mean (± SD) meristem length (right) in Col wild-type and AtCHR23-4ov mutant. (C) Mean (± SD) length of fully elongated cells in elongation zone (left) and mean (± SD) length of the elongation zone (right) in Col wild-type and AtCHR23-4ov mutant. Asterisks indicate significant differences from the wild type: ***, P < 0.001.
Mentions: To determine whether the reduction of root length is due to reduced cell division or reduced cell elongation, we analyzed the size of the meristematic and elongation zone of 6-day-old seedlings. AtCHR23-4ov roots exhibited a normal cellular patterning compared to the wild-type (Figure 3A). For meristem we measured both the length of the meristematic zone and the number of meristematic cortex cells. None of them differ between wild-type and mutant roots (Figure 3B). To further assess the role of cell division, we also used the cell G2-M phase cycle marker pCYCB1;1:CYCB1;1-GUS [29]. No clear difference in the pattern (Additional file1: Figure S2) and number of GUS-positive cells was observed between the wild-type and the over-expressing mutant (data not shown). This is consistent with meristem size of wild-type and mutant (Figure 3B). On the other hand, the mutant showed a significantly shortened (16.8%) elongation zone relative to the wild-type as well as reduced length (23.1%) of the fully elongated cells (Figure 3C). Taken together, these results indicate that the major effect of AtCHR23 up-regulation in the root is the reduction of cell elongation.

Bottom Line: Already modest (2-fold) over-expression of the AtCHR23 ATPase gene in Arabidopsis results in overall reduced growth compared to the wild-type.Detailed analyses show that in the root, the reduction of growth is due to reduced cell elongation.In contrast, the knockout mutation of AtCHR23 does not lead to such visible phenotypic effects.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratory of Molecular Biology, Plant Sciences Group, Wageningen University and Research Centre, Droevendaalsesteeg 1, Wageningen 6708 PB, The Netherlands. ludmila.mlynarova@wur.nl.

ABSTRACT

Background: Plants are sessile organisms that deal with their -sometimes adverse- environment in well-regulated ways. Chromatin remodeling involving SWI/SNF2-type ATPases is thought to be an important epigenetic mechanism for the regulation of gene expression in different developmental programs and for integrating these programs with the response to environmental signals. In this study, we report on the role of chromatin remodeling in Arabidopsis with respect to the variability of growth and gene expression in relationship to environmental conditions.

Results: Already modest (2-fold) over-expression of the AtCHR23 ATPase gene in Arabidopsis results in overall reduced growth compared to the wild-type. Detailed analyses show that in the root, the reduction of growth is due to reduced cell elongation. The reduced-growth phenotype requires sufficient light and is magnified by applying deliberate abiotic (salt, osmotic) stress. In contrast, the knockout mutation of AtCHR23 does not lead to such visible phenotypic effects. In addition, we show that over-expression of AtCHR23 increases the variability of growth in populations of genetically identical plants. These data indicate that accurate and controlled expression of AtCHR23 contributes to the stability or robustness of growth. Detailed RNAseq analyses demonstrate that upon AtCHR23 over-expression also the variation of gene expression is increased in a subset of genes that associate with environmental stress. The larger variation of gene expression is confirmed in individual plants with the help of independent qRT-PCR analysis.

Conclusions: Over-expression of AtCHR23 gives Arabidopsis a phenotype that is markedly different from the growth arrest phenotype observed upon over-expression of AtCHR12, the paralog of AtCHR23, in response to abiotic stress. This demonstrates functional sub-specialization of highly similar ATPases in Arabidopsis. Over-expression of AtCHR23 increases the variability of growth among genetically identical individuals in a way that is consistent with increased variability of expression of a distinct subset of genes that associate with environmental stress. We propose that ATCHR23-mediated chromatin remodeling is a potential component of a buffer system in plants that protects against environmentally-induced phenotypic and transcriptional variation.

Show MeSH
Related in: MedlinePlus